Golang vs C#

This tutorial is intended to help developers learn Go coming from a C# development background and vice versa.

Code examples are availaleble in examples/

Contributing

👍🎉 First off, thank you for taking the time to contribute!

• Please open a pull request for new additions.
• Make sure your code examples lint and build.
• Report issues.

Contents

• Comments
• Variables
• Types
  • String
  • Array
  • Slice
  • Dictionary (C#)
  • Map(Go)
  • Class
  • Struct
  • Interface
  • Enum
• Object vs interface{}
  • object(C#)
  • interface{}(Go)
• Type checking
• Type conversion
• Datetime
• Functions
  • Methods
  • Overloading
  • Multiple return values
  • Default parameters
  • Anonymous functions
• If
• Switch
• For
  • foreach (C#)
  • for range (Go)
• Iterator
• While
• Closures
• Error handling
  • try / catch (C#)
  • exceptions (C#)
  • errors
• throw / panic
• Clean-up
  • finally
  • defer
• Inheritance
• Polymorphism
• Encapsulation
  • Access modifiers
  • Exported types
• Pointers
• Concurrency
  • async / await(C#)
  • goroutines / channels(Go)
• Synchronization
  • Mutex
  • Atomic operations
• Worker pools
• Generics
• Events
• Sorting
• Swapping
• Timeout
• Regular Expressions
• Attributes
  • Tags
• Command-Line Arguments
• Command-Line Flags
• Testing

🔶 Comments

---

C#

using System;

namespace Comments
{
  class Program
  {

    /// <summary>
    ///  Application entry point.  👈 this is an XML Documentation Comment
    /// </summary>
    static void Main(string[] args)
    {
      Console.WriteLine("Comments in C#");

      // Single line comment

      /* multiline
         comment
         in C#
      */

    }
  }
}

Go

package main

import "fmt"

func main() {
	fmt.Println("Comments in Go")

	// Line comment

	/*  General
		   	or
			multiline
	    comment
	*/
}

🔶 Variables

---

A variable is a storage location for holding a value.

C#

using System;

class Program
{
    private static void Main(string[] args)
    {
        // explicit
        int a = 9;

        // implicit
        var b = 9;

        // multiple variables declaration at once
        int c, d, e;
        int x = 1, y = 2, z = 3;

        // Constant (unchangeable and read-only)
        const int i = 7;

        // 📝 Local variables can't be used before assigning them.
        // 📝 Constant variable must be assiged a value at the time of its declaration
    }
}

Go: variables

package main

import "fmt"

func main() {

	// Uninitialized variables are zero-valued
	var a int
	fmt.Println(a) // 0

	var b interface{}
	fmt.Println(b) // nil

	// type is explicitly defined
	var c int = 9

	// type inferred
	var d = true

	// shorthand
	e := "str"

	// multiple variables declaration at once
	var f, g, h int

	// Constant (unchangeable and read-only)
	const i int = 7

	//📝 constant variable must be assiged a value at the time of its declaration

	// all declared variables inside main() must be used
	fmt.Println(c, d, e, f, g, h, i) // 9 true str 0 0 0 7

}

🔶 Types

---

A type defines the blueprint for a value.

C#

using System;

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Types in C#");

        /*
       ♦♦ Predefined types ♦♦
          1. Value types: Numeric, bool, char
          2. Reference types: object , string
      */

        // ♦♦ Numeric types ♦♦

        // Signed integer
        sbyte a = -4;  // 8 bits  –27 to 27–1
        short b = 4;   // 16 bits –215 to 215–1
        int c = 4;     // 32 bits –231 to 231–1
        long d = 4;    // var d = 4L;  64 bits –263 to 263–1

        // Unsigned integer
        byte e = 4;    // 8 bits 0 to 28–1
        ushort f = 4;  // 16 bits 0 to 216–1
        uint g = 4;    // var g = 4U;    32 bits 0 to 232–1
        ulong h = 4;   // var h = 4UL;   64 bits 0 to 264–1

        //Real number
        float j = 0.4F; // 32 bits ± (~10–45 to 1038)
        double k = 4D;  // 64 bits ± (~10–324 to 10308)
        decimal l = 4.0M; // 128 bits ± (~10–28 to 1028)

        var m = 4;   // m is int
        var n = 4.0; // n is double

        // ♦♦ Boolean type ♦♦

        bool o = true;

        // ♦♦ Character type ♦♦

        char p = 'A';

        // ♦♦ String type ♦♦

        string s = "str";

        // ♦♦ Array type ♦♦

        char[] alphabet = new char[26];

        // ♦♦ Object type ♦♦
        // 📝 object is the base class for all types so any type can be upcast to object.

        object obj = 4;

        // composite types

        // ♦ class
        // ♦ struct
        // ♦ interface
        // ♦ enum
    }
}

Go: types

package main

import "fmt"

func main() {
	fmt.Println("Types in Go")

	// ♦♦ Boolean types ♦♦

	var a bool = true

	// ♦♦ Numeric types ♦♦

	var b uint8 = 4  // 8-bit integers (0 to 255)
	var c uint16 = 4 // 16-bit integers (0 to 65535)
	var d uint32 = 4 // 32-bit integers (0 to 4294967295)
	var e uint64 = 4 // 64-bit integers (0 to 18446744073709551615)

	var f int8 = 4  // 8-bit integers (-128 to 127)
	var g int16 = 4 // 16-bit integers (-32768 to 32767)
	var h int32 = 4 // 32-bit integers (-2147483648 to 2147483647)
	var i int64 = 4 // 64-bit integers (-9223372036854775808 to 9223372036854775807)

	var j float32 = 4.0 // IEEE-754 32-bit floating-point numbers
	var k float64 = 4.0 // IEEE-754 64-bit floating-point numbers

	var l complex64 = 3 + 4i  // float32 real and imaginary parts
	var m complex128 = 3 + 4i // float64 real and imaginary parts

	var n byte = 4   //   alias for uint8
	var o rune = 'k' //    alias for int32

	var p uint = 4 // either 32 or 64 bits depending on the underlying platform
	var q int = 4  // either 32 or 64 bits depending on the underlying platform

	// ♦♦ String types ♦♦

	var s string = "str"
	var length int = len(s) // length of s

	// ♦♦ Array types ♦♦
	// 📝 An array is a numbered sequence of elements of a single type
	var r [3]byte = [3]byte{1, 2, 3}

	// ♦♦ Slice types ♦♦
        // 📝 A slice is a descriptor for a contiguous segment of an underlying array
        //     and provides access to a numbered sequence of elements from that array.

	var t []byte = []byte{1, 2, 3}

	// ♦♦ Struct types ♦♦
        // 📝 A struct is a sequence of named elements, called fields,
        //     each of which has a name and a type.

	var v struct{} = struct{}{} // An empty struct.

	var u struct {
		x int
		y int
	} = struct{ x, y int }{3, 4} // A struct with 2 fields.

	// ♦♦ Pointer types ♦♦

	var w *int = new(int)
	var x *int = &q

	// ♦♦ Function types ♦♦

	var fun func() = func() {}

	// ♦♦ Interface types ♦♦

	var z interface{} // z is nil

	// ♦♦ Map types ♦♦

	var mp map[string]int = map[string]int{}

	// ♦♦ Channel types ♦♦

	var ch chan int = make(chan int)

}

string

---

C#

using System;

class Program
{
    static void Main(string[] args)
    {
        // 📝 string represents an immutable sequence of Unicode characters.

        var s = "str";

        var length = s.Length; // gets length of s

        var s1 = "Foo";
        var s2 = "Foo";

        // string is a reference type, but follows value-type semantics

        Console.WriteLine(s1 == s2); // True

        // escape sequences:

        Console.WriteLine("C:\\Users");   // C:\Users
        Console.WriteLine("\"Foo\"");     // "Foo"

        // verbatim string literal:
        Console.WriteLine(@"C:\Users");   // C:\Users

        // string concatenation:

        // 1. using + operator

        var s1s2 = s1 + s2;

        // 2. using System.String's Concat method

        Console.WriteLine(System.String.Concat(s1, s2)); // Concat defined in System.String class

        // 3. using System.Text.StringBuilder, useful when you need to concatenate strings many times

        // String interpolation:

        var day = 27;
        var month = 3;
        var year = 2020;

        Console.WriteLine($"date: {day}/{month}/{year}"); // date: 27/3/2020

        var y = 7.12345;
        Console.WriteLine($"{y:F3}"); // 7.123

        Console.ReadKey();
    }
}

Go: string

package main

import (
	"fmt"
	"strings"
)

func main() {

	// string is:
	// ♦ Immutable: once created, it is impossible to change its contents.
	// ♦ Represented as a collection of UTF-8 characters.

	var s string = "foo"

	var r byte = s[1]

	fmt.Println(r)         // 111 (ascii code for o)
	fmt.Println(string(r)) // o

	// length of s
	fmt.Println(len(s)) // 3

	// strings package defines many string functions such as:

	fmt.Println(strings.Contains(s, "fo"))                   // true
	fmt.Println(strings.ToUpper(s))                          // FOO
	fmt.Println(strings.Repeat("A", 5))                      // AAAAA
	fmt.Println(strings.Split("a-e-i-o-u", "-"))             // [a e i o u]
	fmt.Println(strings.Replace("PreFix", "Pre", "Post", 1)) // PostFix
	fmt.Println(strings.Index(s, "o"))                       // 1

	// string concatenation:

	s1 := "Foo"
	s2 := "Bar"

	// 1: using Builder which minimizes memory copying
	var b strings.Builder
	b.WriteString(s1)
	b.WriteString(s2)

	fmt.Println(b.String()) // FooBar

	// 2: Join method (uses Builder)
	fmt.Println(strings.Join([]string{s1, s2}, "")) // FooBar

	// 3: using + operator
	fmt.Println(s1 + s2) // FooBar

	s1 += s2
	fmt.Println(s1) // FooBar

	// String interpolation:

	day := 27
	month := 3
	year := 2020

	date := fmt.Sprintf("%d/%d/%d", day, month, year)
	fmt.Println(date) // 27/3/2020

}

array

---

C#

using System;

class Program
{
  static void Main(string[] args)
  {
    // 📝 An array represents a fixed number of elements of a single type.

    int[] a = new int[5]; // initializes a 5 elements array with 0 defualt element value

    // checks array length
    Console.WriteLine(a.Length); // 5

    a[0] = 4;

    // array initialization expression:

    int[] b = new int[] { 1, 2, 3, 4, 5 };

    // array is a reference type:

    var a1 = new int[] { 1, 2, 3 };
    var a2 = a1; // a2 & a1 are references to the same array object.

    a2[1] = 5;

    for (int i = 0; i < a1.Length; i++)
      Console.Write(a1[i]); // 153

    // multidimensional arrays

    // two dimensional array of 4 rows and 3 columns.
    int[,] array2D = new int[4, 3] { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 }, { 10, 11, 12 } };

    Console.ReadKey();
  }
}

Go: array

package main

import (
	"fmt"
)

func main() {

	var a [5]int
	fmt.Println(a) // [0 0 0 0 0]

	// checks array length
	fmt.Println(len(a)) // 5

	// update or get element by index
	a[0] = 4

	// initializer syntax
	a1 := [3]int{1, 2, 3} // this is equivalent to 	a1 := [...]int{1, 2, 3}

	a2 := a1 // a2 is assgined to a copy of a1 contents

	a2[1] = 5

	fmt.Println(a1) // [1 2 3]
	fmt.Println(a2) // [1 5 3]

	var a3 *[3]int = &a1 // a3 & a1  points to the same data
	a3[1] = 7

	fmt.Println(a1)  // [1 7 3]
	fmt.Println(*a3) // [1 7 3]

	// multidimensional arrays

	// two dimensional array of 4 rows and 3 columns.
	var array2D [4][3]int
	n := 1
	for i := 0; i < 4; i++ {
		for j := 0; j < 3; j++ {
			array2D[i][j] = n
			n++
		}
	}

	fmt.Println(array2D) // [[1 2 3] [4 5 6] [7 8 9] [10 11 12]]
}

Slice

---

C#

C# doesn't have an equivalent type to golang's slice type.

However, System.Collections.Generic.List is the most similar collection to slice:

• List is implemented using an underlying array.
• Its size is dynamically resized.
• Has O(1) amortized time per insertion.

using System;

class Program
{
  static void Main(string[] args)
  {
    // C#8 Ranges: https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#indices-and-ranges

    var arr = new int[] { 0, 1, 2, 3, 4, 5, 6, 7 };

    var range = arr[3..^1];

    Dump(range);    // 3456
    Dump(arr[..]);  // 01234567
    Dump(arr[..3]); // 012
    Dump(arr[3..]); // 34567

    Console.ReadKey();
  }

  static void Dump(int[] arr)
  {
    foreach (var i in arr)
    {
      Console.Write(i);
    }

    Console.Write("\n");
  }
}

Go: slice

package main

import "fmt"

func main() {

	// 📝 Slice: a descriptor for a contiguous segment of an underlying array
	// its size is dynamically resized.

	a := []int{} // declare a new slice object

	// len(a) function returns slice length (how many items are in the slice)
	fmt.Println(len(a)) // 0

	// cap(a) returns slice total capacity (size of underlying array)
	fmt.Println(cap(a)) // 0

	a = append(a, 1)
	a = append(a, 2)

	fmt.Println(len(a)) // 2
	fmt.Println(cap(a)) // 2

	a = append(a, 3)

	fmt.Println(len(a)) // 3
	fmt.Println(cap(a)) // 4

	a = append(a, 4)
	a = append(a, 5)

	fmt.Println(len(a)) // 5
	fmt.Println(cap(a)) // 8

	/*
		♦ If length becomes equal to capacity then the capacity of the slice
				 increases automatically by reallocating the internal array.
		♦ The size of newly allocated array will be double the size of old one
		 (if len is < 1024).
		♦ In the example above, capacity grows from
		          0 (initial capacity) -> 1 -> 2 -> 4 -> 8
		       or 1 -> 2 -> 4 -> 8 ... n
		♦ Since n + n/2 + n/4 + ...+ 1 = 2n, the amortized time per insertion is O(1)
		     because n insertions take O(n) time.
	*/

	// It's recommened to create slice using make() if size is known beforehand

	size := 5
	s := make([]int, size)

	for i := 0; i < size; i++ {
		s[i] = i
	}

	fmt.Println(s) // [0 1 2 3 4]

	s1 := []int{1, 2, 3}
	s2 := s1 // s2 & s1 points to the same underlying data

	s2[1] = 9

	fmt.Println(s1) // [1 9 3]
	fmt.Println(s2) // [1 9 3]

	// Slicing: constructing a slice from array, slice or string
	//  a[low : high],  low index is inclusive while high is exclusive
	fmt.Println(s1[:])   // [1 9 3]
	fmt.Println(s1[0:2]) // [1 9]
	fmt.Println(s1[:2])  // [1 9]
	fmt.Println(s1[1:])  // [9 3]

	// Removing an elemment from slice
	s3 := []int{1, 2, 3, 4}
	s3 = append(s3[:1], s3[2:]...)
	fmt.Println(s3) // [1 3 4]

	// Strings are read-only slices of bytes
	fmt.Println("test"[1:]) // est
}

Dictionary vs map

---

C#: Dictionary

using System;
using System.Collections.Generic;

class Program
{
    static void Main(string[] args)
    {
        // C# generic Dictionary defined in  System.Collections.Generic namespace
        // It uses a hashtable data structure to store keys and values.

        var colors = new Dictionary<string, string>
        {
             {"White","#FFFFFF" }
            ,{"Red","#FF0000" }
            ,{"Green","#0000FF" }
            ,{"Blue","#008000" }
        };

        Console.WriteLine(colors["Red"]); // #FF0000

        // update value of existing key
        colors["White"] = "#FFF";

        // iterate over dictionary

        foreach (var kv in colors)
        {
            Console.WriteLine($"Code of {kv.Key} is {kv.Value}");
        }

        // check if key is exist

        if (!colors.ContainsKey("Yellow"))
        {
            // adds new key/value pair
            colors.Add("Yellow", "#FFEF00"); // or colors["Yellow"] = "#FFEF00";
        }

        if (!colors.TryGetValue("Yellow", out var _))
        {
            colors.Add("Yellow", "#FFEF00");
        }

        // TryAdd does nothing if key already exist
        if (!colors.TryAdd("Yellow", "#FFEF00"))
        {
            Console.WriteLine("key already exists");
        }
    }
}

Go: Map

package main

import "fmt"

func main() {

    // Initializes an empty map
    m := map[string]int{}

    m["key1"] = 10
    m["key2"] = 20
    m["key3"] = 30

    fmt.Println(m) // map[key1:10 key2:20 key3:30]

    // Deletes key from map
    delete(m, "key2")
    fmt.Println(m) // map[key1:10 key3:30]

    // Update value of existing key
    m["key1"] = 50
    fmt.Println(m) // map[key1:50 key3:30]

    // Iterate over a map
    for key, value := range m {
    	fmt.Println(key, value)
    }

    // Checks if key exists
    if value, ok := m["key1"]; ok {
    	fmt.Println(value) // 50
    }

    // Initializes a map with initial allocation
    m2 := make(map[string]int, 10)
    _ = m2

    // Initializes a map using map literals
    colors := map[string]string{
    	"White": "#FFFFFF",
    	"Red":   "#FF0000",
    	"Green": "#0000FF",
    	"Blue":  "#008000",
    }

    fmt.Println(colors) // map[Blue:#008000 Green:#0000FF Red:#FF0000 White:#FFFFFF]

}

Class

---

📝 A class is a user-defined blueprint or prototype from which objects are created.

C#

Class type is a reference type.

using System;

class Person
{
  // Field
  private string _name;

  // Properties
  public string Name
  {
    set
    {
      _name = value;
    }
    get
    {
      return _name;
    }
  }

  // Auto property
  public DateTime Birthdate { get; set; }

  // Constructors

  // Default constructor used to initialize fields to thier default values
  public Person()
  {
  }

  public Person(string name)
  {
    this.Name = name;
  }

  // Constructor chaining
  public Person(string name, DateTime birthdate)
      : this(name)
  {
    this.Birthdate = birthdate;
  }

  // Method
  public int GetAge()
  {
    // ⚡ This is not a correct way to calculate age from birthdate
    return DateTime.Today.Year - Birthdate.Year;
  }
}

class Program
{
  static void Main(string[] args)
  {
    // Creating new instance of Person class

    // using parameterless constructor
    var p = new Person();

    Console.WriteLine(p.Name);      // null
    Console.WriteLine(p.Birthdate); // 1/1/0001 12:00:00 AM

    // using parameterized constructors

    var p2 = new Person("Adam");
    Console.WriteLine(p2.Name);      // Adam

    var p3 = new Person("Isaac", DateTime.Parse("02/20/2000"));
    Console.WriteLine(p3.Name);      // Isaac
    Console.WriteLine(p3.GetAge());

    var p4 = p3; // p4 & p3 points to the same object
    p4.Name = "Mohamed";
    Console.WriteLine(p3.Name);      // Mohamed

    Console.ReadKey();
  }
}

Go

Go does not have classes.

Struct

---

C#

Struct (or structure) is a value type, useful to hold small data values.

using System;

struct Point
{
  public int X { get; }
  public int Y { get; }

  public Point(int x, int y)
  {
    X = x;
    Y = y;
  }

  public override string ToString() => $"({X}, {Y})";
}

class Program
{
  static void Main(string[] args)
  {
    // Struct instantiation:

    var p = new Point(5, 7);

    Console.WriteLine(p.ToString()); // (5, 7)

    var p2 = p; // p2 is a copy of p

    Console.ReadKey();
  }
}

Go: struct

Struct in Go is a sequence of fields.

package main

import "fmt"

type Person struct {
	name string
	age  int
}

func (p *Person) printAge() {
	fmt.Printf("%v is %v years old\n", p.name, p.age)
}

func main() {

	// Creating a new struct
	p := Person{
		name: "Adam",
		age:  20,
	}

	fmt.Println(p)      // {Adam 20}
	fmt.Println(p.name) // Adam

	p2 := p // p2 is copy of p
	p2.name = "Isaac"
	fmt.Println(p)  // {Adam 20}
	fmt.Println(p2) //{Isaac 20}

	// & prefix yields a pointer to the struct
	p3 := &p // p3 & p poins to the same object
	p3.name = "Mohamed"
	fmt.Println(p)   // {Mohamed 20}
	fmt.Println(*p3) // {Mohamed 20}

	p.printAge() // Mohamed is 20 years old

	// Anonymous struct
	p4 := struct {
		name string
		age  int
	}{
		name: "Nora",
		age:  30,
	}

	fmt.Println(p4) // {Nora 30}

	// Structs are mutable
	p4.age = 50
	fmt.Println(p4) // {Nora 50}
}

Interface

---

C#

• Interface defines a contract.
• A class or a struct can implement multiple interfaces.
• Beginning with C# 8.0, interface can provide a default implementation for members.

using System;

public interface IShape
{
  double GetArea();
}

public interface IDrawable
{
  void Draw();
}

public struct Point
{
  public int X { get; }
  public int Y { get; }

  public Point(int x, int y)
  {
    X = x;
    Y = y;
  }
}

public class Square : IShape
{
  public double Side { get; set; }

  public Square(double side) => Side = side;

  public double GetArea() => Side * Side;
}

// Multiple interface implementations
public class Circle : IShape, IDrawable
{
  public Circle(Point center, double radius)
  {
    Center = center;
    Radius = radius;
  }

  public Point Center { get; set; }
  public double Radius { get; set; }

  public double GetArea() => Math.PI * Radius * Radius;

  public void Draw() => Console.WriteLine("Drawing Circle");
}

internal class Program
{
  private static void PrintArea(IShape shape)
  {
    Console.WriteLine(shape.GetArea());
  }

  private static void Main(string[] args)
  {
    var square = new Square(4);
    PrintArea(square); // 16

    var circle = new Circle(new Point(3, 6), 7);
    PrintArea(circle); // 153.93804002589985

    Console.ReadKey();
  }
}

Go: interface

• Used to group related sets of methods.
• Interfaces are implemented implicitly.
• If a type implements a method with name and signature defined in an interface, then that type implements that interface.

package main

import (
	"fmt"
	"math"
)

type Drawable interface {
	draw()
}

type Shape interface {
	Area() float64
}

type Point struct {
	X, Y int
}

type Square struct {
	side float64
}

type Circle struct {
	center Point
	radius float64
}

// This method means type Circle implements the interface Shape
func (c Circle) Area() float64 {
	return math.Pi * c.radius * c.radius
}

func (c Circle) draw() {
	fmt.Println("Drawing circle")
}

func (s Square) Area() float64 {
	return s.side * s.side
}

func printArea(s Shape) {
	fmt.Println(s.Area())
}

func main() {
	s := Square{side: 4}
	c := Circle{Point{3, 6}, 7}

	// Since both Square & Circle implement Shape interface, we can do the following:
	printArea(s) // 16
	printArea(c) // 153.93804002589985

	var d Drawable = c
	d.draw() // Drawing circle
}

Enum

---

C#

using System;

enum LogLevel
{
  Trace = 1,
  Debug,
  Information,
  Error,
  Warning
}

[Flags]
enum Border
{
  Top,
  Right,
  Bottom,
  Left
}

class Program
{
  static void Main(string[] args)
  {
    var level = LogLevel.Information;
    Console.WriteLine(level);       // Information
    Console.WriteLine((int)level);  // 3
    Console.WriteLine((LogLevel)1); // Trace

    var border = Border.Bottom | Border.Left;

    // Checks if left border has set
    Console.WriteLine((border & Border.Left) == Border.Left); // true

    // Removes left border
    border &= ~Border.Left;
    Console.WriteLine((border & Border.Left) == Border.Left); // false

    Console.ReadKey();
  }
}

Go: enum

package main

import "fmt"

type LogLevel uint8
type Border uint8

const (
	Trace LogLevel = iota + 1
	Debug
	Information
	Error
	Warning
)
const (
	Top    Border = 1 // 1 << iota
	Right         = 2
	Bottom        = 4
	Left          = 8
)

func main() {
	level := Information
	fmt.Println(level)            // 3
	fmt.Println(Information == 3) // true

	border := Bottom | Left

	// Checks if left border has set
	fmt.Println(border&Left == Left) // true

	// Removes left border
	border = border &^ Left
	fmt.Println(border == Bottom) // true

}

🔶 Object vs interface{}

---

C#

Every type in C# derives from object class, so a variable of type object can point to data of any type.

 object[] arr = new object[]
    {
            44,
            4.5,
            "string",
            DateTime.Now,
            true,
            new int[]{1,2,3}
    };

Go: interface{}

• Empty interface is just an interface defined on the fly that has no methods on it.

• Every type in Go implements the empty interface, so a variable of type interface{} can store data of any type.

package main

import (
	"fmt"
	"reflect"
	"time"
)

func main() {

	arr := []interface{}{
		44,
		4.5,
		"string",
		time.Now(),
		true,
		'a',
		[]int{1, 2, 3},
	}
	for _, v := range arr {
		fmt.Println(reflect.TypeOf(v))
	}

}

🔶 Type checking

---

C#

using System;

class Shape { }

class Circle : Shape { }

class Program
{
  static void Main(string[] args)
  {
    // 1. typeof: returns System.Type instance for a type, resolved at compile time.
    // 2. GetType: returns runtime type of an instance.
    // 3. is: returns true if instance is of the same type as given type or drives from it.

    Shape s = new Shape();
    Shape c = new Circle();

    Console.WriteLine(s is Shape);                       // true
    Console.WriteLine(s is Circle);                      // false

    Console.WriteLine(c.GetType() == typeof(Shape));     // false
    Console.WriteLine(c is Shape);                       // true
    Console.WriteLine(c.GetType() == typeof(Circle));    // true
    Console.WriteLine(c is Circle);                      // true

    Console.ReadKey();
  }
}

Go: type checking

package main

import (
	"fmt"
	"reflect"
)

func main() {

	var a int64 = 4

	fmt.Println(reflect.TypeOf(a).Kind() == reflect.Int64)

	var b interface{} = 4

	if _, isInt := b.(int); isInt {
		fmt.Println("i is int")
	}

}

output

true
i is int

🔶 Type conversion

---

C#

using System;

class Circle { }

class Program
{
  static void Main(string[] args)
  {
    var circle = new Circle();

    object obj = circle; // implicit conversion

    // Reference type conversion using is
    if (obj is Circle c)
    {
      Console.WriteLine("obj is Circle");
    }

    Circle c2 = (Circle)obj; // explicit conversion

    var s = "12";
    var a = int.Parse(s);
    var b = Convert.ToInt32(s);

    float d = 4.6F;
    double e = d; // implicit cast
    int f = (int)e; // explicit caset

    Console.WriteLine(f);

    decimal g = (decimal)d;

    Console.ReadKey();
  }
}

output

obj is Circle
4

Go: type conversion

package main

import (
	"fmt"
	"strconv"
)

func main() {

	var a int = 20
	b := float32(a)
	fmt.Printf("%v, %T\n", b, b)

	d := strconv.Itoa(a)
	fmt.Printf("%v, %T\n", d, d)

	e, err := strconv.Atoi("123")
	if err == nil {
		fmt.Printf("%v, %T\n", e, e)
	}

	g, err := strconv.ParseInt("235", 10, 64)
	if err == nil {
		fmt.Printf("%v, %T\n", g, g)
	}
}

output

20, float32
20, string
123, int
235, int64

🔶 Datetime

---

C#

using System;
using System.Globalization;

class Program
{
  static void Main(string[] args)
  {
    Action<object> w = Console.WriteLine;

    w(DateTime.Now);       // computer's date and time, expressed as local time
    w(DateTime.UtcNow);    // computer's date and time, expressed as UTC
    w(DateTimeOffset.Now); // computer's date and time with the offset from UTC
    w(new DateTime(1441, 08, 09, new HijriCalendar())); // 4/2/2020 12:00:00 AM

    var dt = new DateTime(2020, 04, 02, 19, 15, 40, DateTimeKind.Utc);
    w(dt.Year);           // 2020
    w(dt.Month);          // 4
    w(dt.Day);            // 2
    w(dt.DayOfWeek);      // Thursday
    w(dt.DayOfYear);      // 93
    w(dt.Hour);           // 19
    w(dt.Minute);         // 15
    w(dt.Second);         // 40
    w(dt.Millisecond);    // 0
    w(dt.Ticks);          // 637214517400000000
    w(dt.TimeOfDay);      // 19:15:40
    w(dt.Kind);           // Utc

    var unixTimestamp = dt.Subtract(DateTime.UnixEpoch).TotalSeconds;
    w(unixTimestamp);                            // 1585854940
    w(((DateTimeOffset)dt).ToUnixTimeSeconds()); // 1585847740
    w(DateTime.UnixEpoch);                       // 1/1/1970 12:00:00 AM

    w(DateTime.Parse("4-2-2020 7:25:34 PM"));    // 4/2/2020 7:25:34 PM

    var dt1 = DateTime.Now;
    var dt2 = dt1.AddDays(2);
    var diff = dt2.Subtract(dt1);
    w(diff.Days);  // 2
    w(dt2 > dt1);  // true

    // current timezone.
    var zoneInfo = TimeZoneInfo.Local;
    w(zoneInfo.DisplayName);
    w(zoneInfo.StandardName);
    w(zoneInfo.DaylightName);

    // get all timezones
    foreach (var tz in TimeZoneInfo.GetSystemTimeZones())
      w(tz.DisplayName);

    Console.ReadKey();
  }
}

Go: time

package main

import (
	"fmt"
	"time"
)

func main() {
	w := fmt.Println

	w(time.Now()) // 2020-04-02 20:09:15.0305182 +0200 EET m=+0.002996501

	dt := time.Date(2020, 04, 02, 19, 15, 40, 1245678, time.UTC)

	w(dt.Year())       // 2020
	w(dt.Month())      // April
	w(dt.Day())        // 2
	w(dt.Hour())       // 19
	w(dt.Minute())     // 15
	w(dt.Second())     // 40
	w(dt.Nanosecond()) // 1245678
	w(dt.Location())   // UTC
	w(dt.Weekday())    // Thursday

	dt2 := dt.AddDate(0, 0, 2)
	diff := dt2.Sub(dt)
	w(diff) // 48h0m0s

	w(dt2.Before(dt)) // false
	w(dt2.After(dt))  // true
	w(dt2.Equal(dt))  // false

	w(dt.Unix()) // 1585854940

	str := "2020-04-02T19:15:40+00:00"
	layout := "2006-01-02T15:04:05Z07:00"
	dt3, _ := time.Parse(layout, str)
	w(dt3.String()) // 2020-04-02 19:15:40 +0000 +0000

	zone, offset := dt.Zone()
	w(zone, offset) // UTC 0
}

🔶 Functions

---

C#

• In C# functions declared within a type (class, struct or interface).
• Methods can be instane members or static (related to type rather than instances).
• C# supports method and operator overloading.
• Methods can return multiple values by using Tuple, ref or out.
• Methods can passed around as variables or method arguments.

using System;

internal class Program
{
  // Overloaded methods
  public static int Sum(int a, int b) => a + b;

  public static int Sum(int a, int b, int c) => a + b + c;

  // Method with a parameter that takes a variable number of arguments
  public static int Multiply(params int[] values)
  {
    var result = 1;

    for (var i = 0; i < values.Length; i++)
    {
      result *= values[i];
    }

    return result;
  }

  // Method with multiple return values
  public static Tuple<string, int, bool> GetValues()
  {
    return Tuple.Create("some value", 1, false);
  }

  // Func is a delegate type which holds a reference to a method
  public static int Transform(Func<int, int> transformer, int value)
  {
    return transformer(value);
  }

  // Optional parameters
  public static int Increment(int value, int step = 1)
  {
    return value + step;
  }

  public static int Square(int value) => value * value;

  private static void Main(string[] args)
  {
    var square = Transform(Square, 3);
    Console.WriteLine(square);       // 9

    // Anonymous method
    square = Transform(delegate (int value) { return value * value; }, 3);
    Console.WriteLine(square);       // 9

    Console.WriteLine(Sum(1, 2));    // 3
    Console.WriteLine(Sum(1, 2, 3)); // 6

    Console.WriteLine(Increment(1));    // 2
    Console.WriteLine(Increment(1, 5)); // 6

    Console.WriteLine(Multiply(1, 2));       // 2
    Console.WriteLine(Multiply(1, 2, 3));    // 6
    Console.WriteLine(Multiply(1, 2, 3, 4)); // 24

    Console.ReadKey();
  }
}

Go: functions

• Go does not support overloding of methods and operators.
• Go does not support function/method argument default value.
• A Method is a function with a receiver.
• Go supports methods defined on struct types.

package main

import "fmt"

// variadic function: accepts a variable number of arguments
func sum(values ...int) (result int) {

	for _, v := range values {
		result += v
	}

	return // result is a named return value
}

func transform(transformer func(v int) int, value int) int {
	return transformer(value)
}

// multiple return values
func divide(a float32, b float32) (float32, error) {
	if b == 0.0 {
		return 0, fmt.Errorf("Attempted to divide by zero")
	}
	return a / b, nil
}

// Go supports methods defined on struct types.
type user struct {
	name string
}

// value receiver (receives a copy of user instance when called)
func (u user) printName() {
	fmt.Println(u.name)
}

//  pointer receiver (receives a pointer to user instance when called)
func (u *user) printName2() {
	fmt.Println(u.name)
}

func main() {
	fmt.Println(sum(1, 2))    // 3
	fmt.Println(sum(1, 2, 3)) //6

	// Anonymous function
	func(v int) {
		fmt.Println(v) // 4
	}(4)

	// passing func around as variable or parameter
	var square = transform(func(v int) int {
		return v * v
	}, 4)

	fmt.Println(square) // 16

	v, _ := divide(4, 2)
	fmt.Println(v) // 2

	var usr = user{name: "Adam"}

	usr.printName()     // Adam
	(&usr).printName2() // Adam

}

🔶 If

---

C#

using System;

class Program
{
  static void Main(string[] args)
  {
    int a = 4;
    int b = 3;
    int min;

    if (a < b) min = a;
    else min = b;

    // above if statment could be rewritten using ternary operator:
    min = a < b ? a : b;

    if (a == 0)
    {
      Console.WriteLine("x is 0");
    }
    else if (a > 0)
    {
      Console.WriteLine("x is positive");
    }
    else
    {
      Console.WriteLine("x is negative");
    }

    Console.ReadKey();
  }
}

Go: if

package main

import "fmt"

func main() {

	a := 2

	if a < 0 {
		fmt.Println("a is negative")
	} else if a > 0 {
		fmt.Println("a is positive")
	} else {
		fmt.Println("a is 0")
	}

	if b := a + 1; b%2 == 0 {
		fmt.Println("b is even")
	} else {
		fmt.Println("b is odd")

		//  📝 Go doesn't have ternary operator
	}
}

output

a is positive
b is odd

🔶 Switch

---

C#

using System;

class Program
{
  static void Main(string[] args)
  {
    var color = "blue";

    switch (color)
    {
      case "red":
        Console.WriteLine("Red code is #FF0000");
        break;

      case "blue":
        Console.WriteLine("Blue code is #0000FF");
        break;

      default:
        Console.WriteLine("Invalid color");
        break;
    }

    var a = 2;

    switch (a)
    {
      case 1:
      case 2:
      case 3:
        Console.WriteLine("case 1, 2 or 3");
        break;

      case 4:
        Console.WriteLine("case 4");
        break;

      default:
        Console.WriteLine("default case");
        break;
    }

    // Checking for type (C# 7)

    object obj = 4;

    switch (obj)
    {
      case null:
        Console.WriteLine("obj is null");
        break;

      case int v:
        Console.WriteLine("obj is int");
        break;

      case string v:
        Console.WriteLine("obj is string");
        break;

      default:
        Console.WriteLine("obj type is not know");
        break;
    }

    Console.ReadKey();
  }
}

output

Blue code is #0000FF
case 1, 2 or 3
obj is int

Go: switch

package main

import "fmt"

func f1() {
	fmt.Println("Executing f1...")
}
func f2() {
	fmt.Println("Executing f2...")
}
func f3() {
	fmt.Println("Executing f3...")
}

func main() {

	a := 2

	switch {
	case a == 1:
		f1()
	case a == 2:
		f2()
	default:
		f3()
	}

	b := 10

	switch b {
	case 1, 10, 100:
		f1()
	case 2, 20:
		f2()
	default:
		f3()
	}

	switch c := a - 2; {
	case c < 0:
		fmt.Println("c is negative")
	case c > 0:
		fmt.Println("c is positive")
	default:
		fmt.Println("c is 0")
	}

	// fallthrough: transfers control to the first statement of the next case
	i := 1

	switch i {
	case 1:
		fmt.Println("case 1")
		fallthrough
	case 2:
		fmt.Println("case 2")
	default:
		fmt.Println("default")

	}

	// Type switch: compares types rather than values.

	var d interface{} = 4

	switch d.(type) {
	case int:
		fmt.Println("d is int")
	case float32:
		fmt.Println("d is float32")
	default:
		fmt.Println("type is not known")
	}

	// above switch could be rewritten:

	if _, isInt := d.(int); isInt {
		fmt.Println("d is int")
	} else if _, isFloat32 := d.(float32); isFloat32 {
		fmt.Println("d is float32")
	} else {
		fmt.Println("type is not known")
	}
}

output

Executing f2...
Executing f1...
c is 0
case 1
case 2
d is int
d is int

🔶 For

---

C#

using System;

class Program
{
  static void Main(string[] args)
  {
    var arr = new int[] { 1, 2, 3, 4, 5 };

    // different ways for using for to print array elements

    for (var i = 0; i < arr.Length; i++)
    {
      Console.Write(arr[i]);
    }

    Console.Write("\n");

    var j = 0;

    for (; j < arr.Length;)
    {
      Console.Write(arr[j]);
      j++;
    }

    Console.Write("\n");

    var k = 0;

    for (; ; )
    {
      if (k >= arr.Length)
        break;

      Console.Write(arr[k]);
      k++;
    }

    Console.Write("\nodd numbers:");

    // print odd numbers in array
    for (var m = 0; m < arr.Length; m++)
    {
      if (arr[m] % 2 == 0)
        continue;

      Console.Write(arr[m]);
    }
    Console.Write("\n");

    // foreach iterates over any collection that implements IEnumerable
    foreach (var item in arr)
    {
      Console.Write(item);
    }

    Console.ReadKey();
  }
}

output

12345
12345
12345
odd numbers:135
12345

Go: for

package main

import "fmt"

func main() {

	a := 2

	for a < 40 {
		fmt.Printf("%v ", a)
		a *= 2
	}
	fmt.Printf("\n")

	arr := [...]int{1, 2, 3, 4, 5}

	for i := 0; i < len(arr); i++ {
		fmt.Printf("%v ", arr[i])
	}

	fmt.Printf("\n")

	// for range
	for _, v := range arr {
		fmt.Printf("%v ", v)
	}

	// infinite loop
	for {
		// do stuff
		break // break out of loop
	}

	// break statement terminates execution of the innermost loop
	// to terminate execution of outer loop use lables or functions (return)
outerLoop:
	for m := 0; m < 3; i++ {
		for n := 0; n < 5; n++ {
			if m*n == 12 {
				break outerLoop
			}
		}
	}
}

output

2 4 8 16 32
1 2 3 4 5
1 2 3 4 5

🔶 Iterator

---

C#

using System;
using System.Collections.Generic;

class Program
{
  static IEnumerable<int> Where(IEnumerable<int> values, Func<int, bool> predicate)
  {
    foreach (var v in values)
    {
      if (predicate(v))
        yield return v;
    }
  }

  static void Main(string[] args)
  {
    var values = new[] { 1, 2, 3, 4, 5, 6 };
    var odds = Where(values, v => v % 2 == 1);

    foreach (var v in odds)
      Console.Write(v + ", ");

    Console.ReadKey();
  }
}

output

1, 3, 5,

Go: iterator

package main

import (
	"fmt"
	"reflect"
)

type Iterator func() (item interface{}, ok bool)

func Iterate(collection interface{}) Iterator {

	source := reflect.ValueOf(collection)
	len := source.Len()
	i := 0

	if source.Kind() != reflect.Slice && source.Kind() != reflect.Array {
		panic("can't iterate over non-slice or array types")
	}

	return func() (item interface{}, ok bool) {
		ok = i < len
		if ok {
			item = source.Index(i).Interface()
			i++
		}

		return
	}
}

func main() {
	a := []int{1, 2, 3, 4, 5}

	var next Iterator = Iterate(a)

	for item, ok := next(); ok; item, ok = next() {
		fmt.Print(item, ", ")
	}
}

output

1, 2, 3, 4, 5,

🔶 while

---

C#

    var attempt = 1;

    while (attempt <= 3)
    {
      Console.WriteLine($"attempt # {attempt}");
      // do other stuff
      attempt++;
    }

    // use break to exit
    while (true)
    {
	  // do stuff

      break;
    }

    // do ... while: executed at least 1 time
    do
    {
      Console.WriteLine("do while...");
    } while (false);

output

attempt # 1
attempt # 2
attempt # 3
do while...

Go: while

Go doesn't have while keyword but same behavior can be achieved using for.

	// we can get same while behavior using for:
	var attempt = 1

	for attempt <= 3 {
		fmt.Printf("attempt # %v\n", attempt)
		// do other stuff
		attempt++
	}

output

attempt # 1
attempt # 2
attempt # 3

🔶 Closures

---

C#

• Closure is a lambda expression that references parameters of method they're defined in or its local variables.

• These variables survive as long as closure is accessible.

  static Func<int> Sequence(int start = 0)
  {
    // Closure captures method parameter
    return () => start++;
  }

  static void Main(string[] args)
  {
    var stepSize = 2;
    Func<int, int> incrementer = value => value + stepSize;
    stepSize = 5;
    Console.WriteLine(incrementer(3)); // 8

    // The lifetime of captured method parameter is extended to that of the capturing delegate (seq)
    var seq = Sequence();
    Console.WriteLine(seq()); // 0
    Console.WriteLine(seq()); // 1
    Console.WriteLine(seq()); // 2

    var seq2 = Sequence();
    Console.WriteLine(seq2()); // 0

    // Capturing iteration variables

    // Below code is intended to print 01234
    var func = new Func<int>[5];
    for (int i = 0; i < 5; i++)
      func[i] = () => i;

    foreach (var f in func)
      Console.Write(f()); // 55555

    // In this example iteration variable "i" is treaded as it's declared outside the for statement.
    // To get the expected result, define a new variable inside the loop, copy the iteration value to that.
    for (int i = 0; i < 5; i++)
    {
      int k = i;
      func[i] = () => k;
    }

    foreach (var f in func)
      Console.Write(f()); // 01234
	}

Go

• Closure: an anonymous function references an outer variable.

package main

import "fmt"

func sequence() func() int {
	start := 0
	return func() int {
		start++
		return start - 1
	}
}

func main() {

	// Captured variable (start) lifetime is extented to that of the capturing func(), seq.
	seq := sequence()

	fmt.Println(seq()) // 0
	fmt.Println(seq()) // 1
	fmt.Println(seq()) // 2

	seq2 := sequence()
	fmt.Println(seq2()) // 0

	// Capturing iteration variables

	// Below code is intended to print 01234
	// but it prints 55555 because i is captured by anonymous function
	var arr [5]func()

	for i := 0; i < len(arr); i++ {
		arr[i] = func() {
			fmt.Print(i)
		}
	}

	for _, f := range arr {
		f()
	}

	// to get expected result:
	for i := 0; i < len(arr); i++ {
		k := i
		arr[i] = func() {
			fmt.Print(k)
		}
	}

	fmt.Print("\n")

	for _, f := range arr {
		f()
	}
}

🔶 Error handling

---

C#

using System;
using System.IO;

class Program
{
  static void Main(string[] args)
  {
    // All exceptions in c# inherits from System.Exception class

    string filePath = null;
    FileStream stream = null;

    try
    {
      // try block contains the code causing exception

      stream = File.Open(filePath, FileMode.Open);

      //...
    }
    catch (ArgumentException ex) // handles exceptions of type ArgumentException
    {
      Console.WriteLine($"ArgumentException: {ex.Message}");
    }
    catch (Exception ex) // handles any exception
    {
      Console.WriteLine(ex.Message);
    }
    finally
    {
      // will always execute whether an exception is thrown or not.

      if (stream != null)
        stream.Close();
    }
  }
}

Go: error handling

package main

import (
	"errors"
	"fmt"
)

func divide(a int, b int) (int, error) {
	if b == 0.0 {
		return 0, fmt.Errorf("Attempted to divide by zero")
	}
	return a / b, nil
}

func main() {
	// Go doesn't handle exceptions as C# does,
	// there is no tryr/catch, instead errors are returned as a method return value.
	// "error" is a built-in interface, which you can implement to create a custom errors .

	a, b := 4, 0

	result, err := divide(a, b)

	if err != nil {
		// handle error
		fmt.Println("Error: ", err)
	} else {
		fmt.Printf("%v / %v = %v", a, b, result)
	}

	// to create an error:
	_ = fmt.Errorf("error message")
	// or
	_ = errors.New("error message")

}

output

Error:  Attempted to divide by zero

🔶 throw / panic

---

C#: throw

 static void Display(string name)
  {
    if (string.IsNullOrEmpty(name))
      throw new ArgumentNullException(nameof(name), "name can't be null or empty");

    Console.WriteLine($"Hello, {name}");
  }

  static void Main(string[] args)
  {
    // throw: rethrows same exception and preserves original stack trace.
    // throw ex: rethrows exception and resets the stack trace.
    try
    {
      var name = Console.ReadLine();
      Display(name);
    }
    catch (Exception ex)
    {
      //  throw;
      //  throw ex;
      Console.WriteLine(ex.Message);
    }
  }

Go: panic

package main

import (
	"fmt"
)

func divide(a int, b int) int {
	if b == 0.0 {
		// panic is similar to C#'s exceptions, it's a run-time error.
		// panic() function terminates the flow of control and starts panicking.
		panic("Attempted to divide by zero")
	}
	return a / b
}

func main() {
	// recover(): regains control of a panicking goroutine.
	// defer function always run even if the program panics.
	defer func() {
		if x := recover(); x != nil {
			fmt.Println("run time panic: ", x)
		}
	}()

	fmt.Println("main start")
	_ = divide(4, 0)
}

🔶 Clean up

---

C#

// "using" statement is used to automatically dispose an object once
//     using statement is exited (by reaching block end or by an exception).
// The objects specified within the using block must implement the IDisposable interface.
// IDisposable interface contains Dispose method which can be invoked when object is no longer needed.

using (var fileStream = File.Open("path/to/file", FileMode.Open))
{
   // ....
}

// this is equivalent to:
FileStream fs = null;

try
{
   fs = File.Open("path/to/file", FileMode.Open);

   // ...
}
finally
{
   if (fs != null)
      fs.Dispose();
}

Go: cleanup

package main

import (
	"fmt"
	"os"
)

func main() {

	file, err := os.Create("/path/to/file")

	if err != nil {
		fmt.Println(err)
	}

	// Defere is used for clean-up activities
	// Deferred function calls are executed in
	// Last In First Out order after the surrounding function returns

	defer file.Close()

	// write to  file
	fmt.Fprintln(file, "test test...")

}

🔶 Inheritance

---

• Inheritance is "is a" relationship: 🐶 is an Animal.
• Method overriding: change the implementation of a function
  in the derived class that is defined in the base class.
• C# doesn't support multiple inheritance through classes.
• Any class or struct can implement multiple interfaces.
• Structs don't support inheritance.

C#

using System;

internal class Base
{
  public virtual void SomeMethod() => Console.WriteLine("I am Base");
}

internal class DerivedA : Base
{
  // this method overrides Base's SomeMethod implementation.
  public override void SomeMethod() => Console.WriteLine("I am Derived_A");
}

internal class DerivedB : DerivedA
{
  public new void SomeMethod() => Console.WriteLine("I am Derived_B");
}

internal class Program
{
  private static void Main(string[] args)
  {
    Base baseObj = new Base();
    Base ba = new DerivedA();
    Base bb = new DerivedB();
    DerivedB b = new DerivedB();

    baseObj.SomeMethod();
    ba.SomeMethod();
    bb.SomeMethod();
    b.SomeMethod();

    Console.ReadKey();
  }
}

output

I am Base
I am Derived_A
I am Derived_A
I am Derived_B

Go: inheritance

Go doesn’t support inheritance, but supports struct embed­ding and composition to reuse code.

package main

import "fmt"

type Animal struct {
	name string
	age  int
}

// struct embed­ding
type Dog struct { // 🐶
	Animal
	breed string
}

// struct composition
type Cat struct { // 🐱
	pet Animal
}

func (a *Animal) Description() string {
	return fmt.Sprintf("name: %v, age: %v", a.name, a.age)
}

func (a *Animal) Sleep() {
	fmt.Printf("%v is sleeping\n", a.name)
}

func (c *Cat) Sleep() {
	c.pet.Sleep()
}

func main() {
	dog := Dog{Animal: Animal{name: "Max", age: 3}, breed: "Basenji"}
	fmt.Println(dog.Description())
	dog.Sleep()

	cat := Cat{pet: Animal{name: "Kitty", age: 2}}

	fmt.Println(cat.pet.Description())
	cat.Sleep()
}

output

name: Max, age: 3
Max is sleeping
name: Kitty, age: 2
Kitty is sleeping

🔶 Polymorphism

---

C#

• Compile-time or static poly­mor­phism:
  • method/operator overloading.
• Runtime poly­mor­phism:
  • method overriding through inheritance.

A polymorphic behavior can be achieved by using features like variance (covariance and contravariance)

Go

A polymorphic behavior can be achieved by using interfaces.

package main

import (
	"fmt"
	"math"
	"reflect"
)

type Shape interface {
	Area() float64
}

type Square struct {
	side float64
}

type Circle struct {
	radius float64
}

func (c Circle) Area() float64 {
	return math.Pi * c.radius * c.radius
}

func (s Square) Area() float64 {
	return s.side * s.side
}

func displayArea(shape Shape) {
	fmt.Printf("area of %v is %v\n", reflect.TypeOf(shape).Name(), shape.Area())
}

func main() {

	shapes := []Shape{Square{3}, Circle{3}}
	for _, v := range shapes {
		displayArea(v)
	}
}

output

area of Square is 9
area of Circle is 28.274333882308138

🔶 Encapsulation

---

C#

C# has 5 access modifiers used to limit type or type member accessibility:

• public: accessible within the containing assembly or any other assemblies.
• internal: accessible within the contatining assembly (or friend assemblies).
• private: accessible only within the containing struct or class.
• protected: accessible only within the containing struct or class or subclasses.
• protected internal: accessible only within the containing assembly or subclasses from any assembly.

public class A // A is accessed by code from any assembly.
{
  // _field1 is accessible only within A class ( fields are private by default).
  int _field1;
  protected internal int _field2;
  protected virtual void MethodA() => _; // accessible only within A or B classes
}

class B : A // B is internal (class by default is internal)
{
  protected void MethodB()
  {
    base._field1; // error: can't access _field1
    base.MethodA();
  }
}

// if C is defined in a different assembly than A's assembly, it must subclass A to access _field2
internal class C
{
  public C()
  {
    var a = new A();
    var x = a._field2;
    a.MethodA(); // error: can't access MethodA
  }
}

Go: access rights

A package is the smallest unit of private encap­sulation in Go.

Identifiers in Go are:

• Exported: an exported identifier starts with a capital letter and can be accessed from another different package.

• Unexported: unexported identifier starts with a lowercase letter and can only be accessed within the same package.

package main

import "fmt"

// unexported method, accessible only within 'main' package
func saySomething() {
	fmt.Println("Hi......")
}

// exported type, visible to other packages
type ExportedStruct struct {
  field1 string // unexported field
  Field2 string // exported field
}

func main() {
	saySomething()
}

🔶 Pointers

---

C#

When you pass a variable to a method:

• if it's value type, you pass a copy of variable's value.

• if it's reference type, you pass a copy of reference to the object.

• ref keyword is used to pass variable by reference.

• By default, C# does not support pointer arithmetic.

• Pointers can be used only inside an unsafe context, using unsafe keword.

using System;

class Cat // 🐱
{
  public string Name { get; set; }
}

class Program
{
  static void RenameCat(Cat cat) => cat.Name = "Max";

  static void PassReferenceTypeByValueTest(Cat c) => c = null;

  static void PassReferenceTypeByReferenceTest(ref Cat c) => c = null;

  static void PassValueTypeByReferenceTest(ref int n) => n++;

  static void PassValueTypeByValueTest(int n) => n++;

  static void Main(string[] args)
  {
    var cat = new Cat { Name = "Kitty" };

    // passing reference rypes by value: passing a copy of cat reference
    RenameCat(cat);
    Console.WriteLine(cat.Name);

    PassReferenceTypeByValueTest(cat);
    Console.WriteLine(cat is null);

    // Passing reference rypes by reference
    PassReferenceTypeByReferenceTest(ref cat);
    Console.WriteLine(cat is null);

    // value types:

    var a = 1;

    // Passing value types by value
    PassValueTypeByValueTest(a);
    Console.WriteLine(a);

    // Passing value types by reference
    PassValueTypeByReferenceTest(ref a);
    Console.WriteLine(a);

    // Pointers:
    int b = 5;

    // this code won't compile without unsafe option
    unsafe
    {
      int* p = &b;
      Console.WriteLine(*p);

      *p += 1;
      Console.WriteLine(*p);
    }

    Console.ReadKey();
  }
}

output

Max
False
True
1
2
5
6

Go: pointers

• For safety reasons, Go doesn't suport pointer arithmetic.
• You can get around this by using unsafe package

package main

import "fmt"

func valTest(v int) {
	v = 5
}

func pointerTest(v *int) {
	// pointer dereferencing
	*v = 5
}

type Cat struct{ name string } // 🐱

// value receiver doesn't mutate state
func (c Cat) valReceiverTest() {
	c.name = "Max"
}

// pointer receiver mutates state
func (c *Cat) pointerReceiverTest() {
	c.name = "Max"
}

func main() {

	a := 2

	// passing variables by value copies the value.
	valTest(a)
	fmt.Println(a)

	// &a: address operator, generates a pointer to a
	pointerTest(&a)

	fmt.Println(a)

	c := Cat{name: "Kitty"}
	// passes copy of c to valReceiverTest method
	c.valReceiverTest()
	fmt.Println(c.name)

	// passes address of c to pointerReceiverTest method
	c.pointerReceiverTest()
	fmt.Println(c.name)
}

output

2
5
Kitty
Max

🔶 Concurrency

---

C#

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using Newtonsoft.Json;

internal class Program
{
  private class QuoteEntity
  {
    public string Quote { get; set; }
    public string Author { get; set; }
  }

  private static void DisplayQuote(QuoteEntity quote) =>
      Console.WriteLine($"quote: {quote.Quote}\nauthor: {quote.Author}\n");

  private static async Task<QuoteEntity> GetRandomQuoteAsync()
  {
    var path = "http://quotes.stormconsultancy.co.uk/random.json";

    var json = await new HttpClient().GetStringAsync(path);

    return JsonConvert.DeserializeObject<QuoteEntity>(json);
  }

  private static async Task Main(string[] args)
  {
    // Multithreading: using multiple threads.
    // C# has a high-level features that abstracts a way the concept of threads,
    // so mostly, we don't need to create a thread using new keyword.
    var t1 = new Thread(() => Console.WriteLine("Thread 1"));
    t1.Start();
    t1.Join();

    // Asynchronous programming

    var quote = await GetRandomQuoteAsync();
    DisplayQuote(quote);

    var task = Task.Run(GetRandomQuoteAsync);
    quote = await task;
    DisplayQuote(quote);

    // Waiting for many tasks to complete
    var tasks = new Task<QuoteEntity>[] {
            GetRandomQuoteAsync(),
            GetRandomQuoteAsync()
        };

    var quotes = await Task.WhenAll(tasks);

    foreach (var q in quotes)
      DisplayQuote(q);

    Console.ReadKey();
  }
}

Go: concurrency

• Goroutine is a function that is capable of running concurrently with other functions.
• Channel is a pipeline for sending and receiving data.
• Channels provide a way for one goroutine to send structured data to another.
• By default, Go uses CPU threads equal to available cores.

Threads vs Goroutines

Thread	Goroutine
Managed by OS	Managed by Go runtime
Has its own execution stack	Has its own execution stack
Fixed stack size (around 1 MB)	Variable stack size (starts from 2 KB)

package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"sync"
)

type Quote struct {
	Quote  string `json:"quote"`
	Author string `json:"author"`
}

func parseBody(r *http.Response, x interface{}) {
	defer r.Body.Close()
	body, err := ioutil.ReadAll(r.Body)
	if err != nil {
		log.Fatal(err)
		return
	}

	if err = json.Unmarshal(body, x); err != nil {
		log.Fatal(err)
	}
}

func getRandomQuote() Quote {
	res, err := http.Get("http://quotes.stormconsultancy.co.uk/random.json")
	if err != nil {
		log.Fatal(err)
	}
	q := Quote{}
	parseBody(res, &q)

	return q
}

func displayQuotes(ch <-chan Quote) {
	for {
		select {
		case quote := <-ch:
			fmt.Printf("%+v\n", quote)
		case <-doneCh:
			break
		}
	}
}

var doneCh = make(chan struct{})

func main() {
	quotesCount := 5
	quotesCh := make(chan Quote, quotesCount)

	// WaitGroup is similar to C#'s Task.WhenAll,
	// used to wait for multiple goroutines to finish
	wg := &sync.WaitGroup{}

	go displayQuotes(quotesCh)

	// get random quotes
	wg.Add(quotesCount)
	for i := 0; i < quotesCount; i++ {
		go func(ch chan<- Quote, wg *sync.WaitGroup) {
			defer wg.Done()
			quote := getRandomQuote()
			ch <- quote
		}(quotesCh, wg)
	}

	wg.Wait()
	doneCh <- struct{}{}
}

🔶 Synchronization

---

Mutex

C#

Grants exclusive access to a shared resource, can be used for interprocess synchronization.

using System;
using System.Threading;

class Program
{
  private static readonly Mutex mutex = new Mutex();

  static void DoSomething()
  {
    // Wait until it is safe to enter.
    mutex.WaitOne();
    Console.WriteLine($"{Thread.CurrentThread.Name} has entered in the protected area");

    // Waits 1 second
    Thread.Sleep(TimeSpan.FromSeconds(1));

    Console.WriteLine($"{Thread.CurrentThread.Name} is leaving the protected area\r\n");
    // Release the mutex
    mutex.ReleaseMutex();
  }

  static void Main(string[] args)
  {
    for (int i = 0; i < 4; i++)
      new Thread(new ThreadStart(DoSomething))
      {
        Name = $"Thread{i + 1}"
      }
      .Start();
  }
}

output: note that threads can execute in different order for each run

Thread2 has entered in the protected area
Thread2 is leaving the protected area

Thread4 has entered in the protected area
Thread4 is leaving the protected area

Thread1 has entered in the protected area
Thread1 is leaving the protected area

Thread3 has entered in the protected area
Thread3 is leaving the protected area

Go: mutex

Mutex is used to safely access data across multiple goroutines.

package main

import (
	"fmt"
	"sync"
)

type SafeCounter struct {
	mutex   sync.Mutex
	Counter int
}

func (c *SafeCounter) Increment() {
	c.mutex.Lock()
	c.Counter++
	c.mutex.Unlock()
}

func (c *SafeCounter) Reset() {
	// we don't need the lock since assignment is atomic.
	c.Counter = 0
}

func main() {
	wg := sync.WaitGroup{}
	wg.Add(50)

	sc := SafeCounter{}
	for i := 0; i < 50; i++ {
		go func() {
			for c := 0; c < 1000; c++ {
				sc.Increment()
			}
			wg.Done()
		}()
	}

	wg.Wait()
  fmt.Println(sc.Counter)

  	// RWMutex: a reader/writer mutual exclusion lock.
	// The lock can be held by an arbitrary number of readers or a single writer.
	_ = sync.RWMutex{}
}

output

50000

Atomic operations

---

C#

System.Threading.Interlocked class provides atomic operations for variables that are shared by multiple threads.

/// <summary>
/// Thread safe Id generator
/// </summary>
class IdGenerator
{
    private static int _lastId;

    // returns a new id with a unique value
    public static int GetNextId()
    {
        return Interlocked.Increment(ref _lastId);
    }
}

Go

package main

import (
	"fmt"
	"sync"
	"sync/atomic"
)

type SafeCounter struct {
	Counter int64
}

func (c *SafeCounter) Increment() {
	atomic.AddInt64(&c.Counter, 1)
}

func (c *SafeCounter) Reset() {
	c.Counter = 0
}

func main() {

	sc := SafeCounter{}
	wg := sync.WaitGroup{}

	wg.Add(50)
	for i := 0; i < 50; i++ {
		go func() {
			for c := 0; c < 1000; c++ {

				sc.Increment()
			}
			wg.Done()
		}()
	}

	wg.Wait()

	fmt.Println(sc.Counter == 50*1000) // true
}

🔶 Worker pools

---

C#

C# has a Threadpool class.

Go

package main

import (
	"fmt"
	"runtime"
	"sync"
	"time"
)

func worker(id int, taskQueue <-chan func(w int)) {
	for fun := range taskQueue {
		fun(id)
	}
}

func main() {

	maxWorkers := runtime.GOMAXPROCS(0)
	taskQueue := make(chan func(w int), 1)
	wg := sync.WaitGroup{}

	wg.Add(maxWorkers)
	for w := 1; w <= maxWorkers; w++ {
		go func(id int) {
			worker(id, taskQueue)
			wg.Done()
		}(w)
	}

	for i := 1; i <= 7; i++ {
		t := i
		taskQueue <- func(w int) {
			fmt.Printf("Worker # %v is executing task # %v\n", w, t)
			time.Sleep(time.Second * 2)
		}
	}

	close(taskQueue)
	wg.Wait()
}

output looks similar to the following if executed in a 4 core CPU:

Worker # 3 is executing task # 3
Worker # 2 is executing task # 2
Worker # 4 is executing task # 4
Worker # 1 is executing task # 1
Worker # 3 is executing task # 5
Worker # 2 is executing task # 6
Worker # 4 is executing task # 7

🔶 Generics

---

C#

using System;
// generic stack
class Stack<T>
{
  public int Count { get; private set; }
  public int Capacity { get; private set; }
  private T[] _items = new T[0];

  public Stack() { }
  public Stack(int capacity) => Capacity = capacity;

  public void Push(T value)
  {
    if (_items.Length == Count) _items = IncreaseCapacity(_items, Count);
    _items[Count++] = value;
  }

  public T Peek()
  {
    if (Count == 0) throw new InvalidOperationException("The stack is empty");
    return _items[Count - 1];
  }

  public T Pop()
  {
    if (Count == 0) throw new InvalidOperationException("The stack is empty");
    var item = _items[--Count];
    _items[Count] = default;
    return item;
  }

  private T[] IncreaseCapacity(T[] array, int currentCapacity)
  {
    Capacity = currentCapacity == 0 ? 4 : currentCapacity * 2;
    var arr = new T[Capacity];
    if (currentCapacity != 0) Array.Copy(array, arr, array.Length);
    return arr;
  }
}

class Program
{
  static void Main(string[] args)
  {
    var intStack = new Stack<int>();
    var stringStack = new Stack<string>();
  }
}

Go

• Go doesn't have generics.
• However, you can instantiate an array, slice or map with an arbitrary element types.

ints := []int{1, 2, 3, 4}
strings := []string{"A", "B", "C"}

🔶 Events

---

C#

using System;

class EmailUpdatedEventArgs : EventArgs
{
  public readonly string OldEmail, NewEmail;

  public EmailUpdatedEventArgs(string oldEmail, string newEmail)
  {
    OldEmail = oldEmail;
    NewEmail = newEmail;
  }
}

class Person
{
  public string Username { get; }

  private string _email;

  public string Email
  {
    get { return _email; }
    set
    {
      if (_email == value) return;
      var oldEmail = _email;
      _email = value;
      EmailUpdated(this, new EmailUpdatedEventArgs(oldEmail, _email));
    }
  }

  public Person(string username) => Username = username;

  public event EventHandler<EmailUpdatedEventArgs> EmailUpdated = delegate { };
}

class Program
{
  static void Main(string[] args)
  {
    var person = new Person("Adam");
    person.EmailUpdated += PersonEmailUpdated;
    person.Email = "[email protected]";
    person.Email = "[email protected]";
    // unsubscribe
    person.EmailUpdated -= PersonEmailUpdated;
    person.Email = "[email protected]";
  }

  static void PersonEmailUpdated(object sender, EmailUpdatedEventArgs e)
  {
    var person = sender as Person;
    var msg = $"{person.Username} updated his email from '{e.OldEmail}' to '{e.NewEmail}'";
    Console.WriteLine(msg);
  }
}

output

Adam updated his email from '' to '[email protected]'
Adam updated his email from '[email protected]' to '[email protected]'

Go: events

• Go doesn't support events as a language feature as C# does.
• Events in Go can be implemented using channels, as in this package.

package main

import (
	"fmt"
)

type EventEmitter map[string][]chan string

type Person struct {
	username string
	email    string
	emitter  EventEmitter
}

func (p *Person) UpdateEmail(email string) bool {
	if p.email != email {
		msg := fmt.Sprintf("%v updated his email from '%v' to '%v'", p.username, p.email, email)
		p.email = email
		p.emitter.Emit("email-updated", msg)
		return true
	}
	return false
}

func (p *Person) addEmailUpdateListener(ch chan string) {
	p.emitter.addEventListener("email-updated", ch)
}

func (p *Person) removeEmailUpdateListener(ch chan string) {
	p.emitter.removeEventListener("email-updated", ch)
}

func (emitter EventEmitter) addEventListener(event string, ch chan string) {
	if _, ok := emitter[event]; ok {
		emitter[event] = append(emitter[event], ch)
	} else {
		emitter[event] = []chan string{ch}
	}
}
func (emitter EventEmitter) removeEventListener(event string, ch chan string) {

	if _, ok := emitter[event]; ok {
		listeners := emitter[event]
		for i := range listeners {
			if listeners[i] == ch {
				emitter[event] = append(listeners[:i], listeners[i+1:]...)
				break
			}
		}
	}
}

func (emitter EventEmitter) Emit(event string, msg string) {
	if _, ok := emitter[event]; ok {
		for _, handler := range emitter[event] {
			go func(handler chan string) {
				handler <- msg
			}(handler)
		}
	}
}

func main() {

	p := Person{
		username: "Adam",
		email:    "[email protected]",
		emitter:  EventEmitter{},
	}

	listeners := []chan string{
		make(chan string),
		make(chan string),
	}
	for i, ch := range listeners {
		p.addEmailUpdateListener(ch)
		go func(c chan string, j int) {
			for {
				msg := <-c
				fmt.Printf("listener#%v: %v\n", j, msg)
			}
		}(ch, i)
	}

	p.UpdateEmail("[email protected]")
	// Removes listener#0
	p.removeEmailUpdateListener(listeners[0])
	p.UpdateEmail("[email protected]")

	fmt.Scanln()
}

output

listener#0: Adam updated his email from '[email protected]' to '[email protected]'
listener#1: Adam updated his email from '[email protected]' to '[email protected]'
listener#1: Adam updated his email from '[email protected]' to '[email protected]'

🔶 Sorting

---

C#

using System;
using System.Linq;
// 🐱
class Cat : IComparable<Cat>
{
  public string Name { get; set; }
  public int Age { get; set; }

  public Cat(string name, int age)
  {
    Name = name;
    Age = age;
  }

  public override string ToString() => $"{Name}-{Age} ";

  public int CompareTo(Cat other)
  {
    // sort by age then name
    var result = Age.CompareTo(other.Age);
    if (result == 0) result = Name.CompareTo(other.Name);
    return result;
  }
}

static class Program
{
  static void Main(string[] args)
  {
    // Sort array in ascending order
    var arr1 = new[] { 5, 2, 9, -2, 0, 4 };
    Array.Sort(arr1);
    arr1.Dump();

    // Sort array in descending order
    var arr2 = new[] { 5, 2, 9, -2, 0, 4 };
    Array.Sort(arr2, (v1, v2) => v2 - v1);
    arr2.Dump();

    // Sort using LINQ
    var arr3 = new[] { "D", "A", "E", "B", "C" };
    arr3 = arr3.OrderBy(v => v).ToArray();
    arr3.Dump();

    // Sort composite objects
    var arr4 = new[]{
            new Cat("Max",4),
            new Cat("Max",3),
            new Cat("Angel",1),
            new Cat("Kitty",3),
        };
    Array.Sort(arr4); // sort by name then age
    arr4.Dump();

    Console.ReadKey();
  }

  static void Dump<T>(this T[] arr)
  {
    foreach (var v in arr)
      Console.Write(v + " ");

    Console.Write("\n");
  }
}

output

-2 0 2 4 5 9
9 5 4 2 0 -2
A B C D E
Angel-1  Kitty-3  Max-3  Max-4

Go

package main

import (
	"fmt"
	"sort"
)

type Cat struct { // 🐱
	Name string
	Age  int
}

// implements sort.Interface.
type ByAgeThenName []Cat

func (c ByAgeThenName) Len() int { return len(c) }
func (c ByAgeThenName) Less(i, j int) bool {
	if c[i].Age < c[j].Age {
		return true
	}
	if c[i].Age > c[j].Age {
		return false
	}
	return c[i].Name < c[j].Name

}
func (c ByAgeThenName) Swap(i, j int) { c[i], c[j] = c[j], c[i] }

func main() {
	// Sort in ascending order
	arr1 := []int{5, 2, 9, -2, 0, 4}
	sort.Ints(arr1)
	fmt.Println(arr1)

	// Sort slice in descending order
	arr2 := []int{5, 2, 9, -2, 0, 4}
	sort.Sort(sort.Reverse(sort.IntSlice(arr2)))
	fmt.Println(arr2)

	// Sort strings
	arr3 := []string{"D", "A", "E", "B", "C"}
	sort.Strings(arr3)
	fmt.Println(arr3)

	// Sort custom objects
	arr4 := []Cat{
		Cat{"Max", 4},
		Cat{"Max", 3},
		Cat{"Angel", 1},
		Cat{"Kitty", 3},
	}
	sort.Sort(ByAgeThenName(arr4)) // sort by Age then Name
	fmt.Println(arr4)
}

output

[-2 0 2 4 5 9]
[9 5 4 2 0 -2]
[A B C D E]
[{Angel 1} {Kitty 3} {Max 3} {Max 4}]

🔶 Swapping

---

C#

using System;

class Program
{
  static void Swap(ref int a, ref int b)
  {
    var temp = a;
    a = b;
    b = temp;
  }

  static void Main(string[] args)
  {
    var a = 3;
    var b = 5;
    Swap(ref a, ref b);
    Console.WriteLine($"{a} {b}"); // 5 3
  }
}

Go

package main

import "fmt"

func main() {
	a := 3
	b := 5

	b, a = a, b

	fmt.Println(a, b) // 5 3
}

🔶 Timeout

---

C#

using System;
using System.Threading;
using System.Threading.Tasks;

class Program
{
  static async Task DoSomethingAsync()
  {
    await Task.Delay(TimeSpan.FromSeconds(3));
    Console.WriteLine("DoSomethingAsync is done.");
  }

  static async Task TrySomethingAsync(TimeSpan timeout)
  {
    var cts = new CancellationTokenSource();
    cts.CancelAfter(timeout);

    for (int i = 0; i < 100; i++)
    {
      cts.Token.ThrowIfCancellationRequested();

      // Simulate some work
      await Task.Delay(TimeSpan.FromSeconds(1));
    }
  }

  static async Task Main(string[] args)
  {
    // 1. Implementing timeout using Task.WhenAny:
    var timeoutTask = Task.Delay(TimeSpan.FromSeconds(2));
    var completedTask = await Task.WhenAny(timeoutTask, DoSomethingAsync());

    if (completedTask == timeoutTask)
      // 📝 DoSomethingAsync isn't cancelled, we just won't wait for it to complete.
      Console.WriteLine("DoSomethingAsync is timed out");

    // 2. Implementing timeout using cancellation tokens:
    try
    {
      await TrySomethingAsync(TimeSpan.FromSeconds(2));
      Console.WriteLine("TrySomethingAsync finished without cancelling.");
    }
    catch (OperationCanceledException)
    {
      Console.WriteLine("TrySomethingAsync is cancelled.");
    }
  }
}

output

DoSomethingAsync is timedout
DoSomethingAsync is done.
Task is cancelled.

Go

package main

import (
	"fmt"
	"time"
)

func main() {

  ch := make(chan string, 1)

	go func() {
		// Simulate some work.
		time.Sleep(2 * time.Second)
		ch <- "done"
	}()

	select {
	case res := <-ch:
		fmt.Println(res)
	case <-time.After(1 * time.Second):
		fmt.Println("timed out")
	}
}

output

timed out

🔶 Regular Expressions

---

C#

using System;
using System.Text.RegularExpressions;

class Program
{
  static void Main(string[] args)
  {
    // Alphanumeric string that may include _ and – having a length of 3 to 16 characters.
    var regex = new Regex("^[a-z0-9_-]{3,16}$");
    Console.WriteLine(regex.IsMatch("Max"));
    Console.WriteLine(regex.IsMatch("max"));

    // To ignore case use RegexOptions.IgnoreCase or update pattern to ^[A-Za-z0-9_-]{3,16}$
    regex = new Regex("^[a-z0-9_-]{3,16}$", RegexOptions.IgnoreCase);
    Console.WriteLine(regex.IsMatch("Max"));

    // Split string
    var str = "A1B2C3DE4F5";
    regex = new Regex("[0-9]+", RegexOptions.IgnoreCase);

    foreach (var s in regex.Matches(str))
      Console.Write($"'{s}', ");

    Console.Write("\n");

    var strings = Regex.Split(str, "[a-z]+", RegexOptions.IgnoreCase | RegexOptions.Compiled);
    foreach (var s in strings)
      Console.Write($"'{s}', ");

    Console.ReadKey();
  }
}

output

False
True
True
'1', '2', '3', '4', '5',
'', '1', '2', '3', '4', '5',

Go

package main

import (
	"fmt"
	"regexp"
)

func main() {
	match, _ := regexp.MatchString("^[a-z0-9_-]{3,16}$", "max")
	fmt.Println(match)

	regex, _ := regexp.Compile("p([a-z]+)ch")
	fmt.Println(regex.MatchString("peach"))
	fmt.Println(regex.FindString("peach punch"))

	regex, _ = regexp.Compile("[0-9]+")
	fmt.Println(regex.FindAllString("A1B2C3DE4F5", -1))

}

output

true
true
peach
[1 2 3 4 5]

🔶 Attributes

---

• Attributes are used to convey information/metadata to runtime about various code elements such as methods, assemblies, properties, types.
• Attributes are discoverable at runtime via reflection.

C#

using System;

[AttributeUsage(AttributeTargets.Property)]
class StringLengthAttribute : Attribute
{
  public int MinLength { get; }
  public int MaxLength { get; }

  public StringLengthAttribute(int minLength, int maxLength)
  {
    MinLength = minLength;
    MaxLength = maxLength;
  }
}

class Person
{
  [StringLength(minLength: 3, maxLength: 50)]
  public string Name { get; set; }
}

class Program
{
  static void Main(string[] args)
  {
    var propertyInfos = typeof(Person).GetProperties();

    foreach (var p in propertyInfos)
    {
      var att = (StringLengthAttribute)Attribute.GetCustomAttribute(p, typeof(StringLengthAttribute));
      if (att != null)
      {
        Console.Write($"The max length for the {p} property is: {att.MaxLength}\n");
        Console.Write($"The min length for the {p} property is: {att.MinLength}\n");
      }
    }
  }
}

output

The max length for the System.String Name property is: 50
The min length for the System.String Name property is: 3

Go: tags

Go doesn't have attributes, but have struct tags which are discoverable via reflection.

package main

import(
"fmt"
"reflect"
)

type  Person struct{
	Name string `json:"name"`
}

func main()  {

	t:= reflect.TypeOf(Person{})
	f, _ := t.FieldByName("Name")
	fmt.Println(f.Tag) // json:"name"
}

🔶 Command-Line Arguments

---

C#

using System;

class Program
{
  static void Main(string[] args)
  {
    if (args.Length > 0)
    {
      foreach (var arg in args)
        Console.Write(arg + " ");
    }
  }
}

output

❯ cli_args.exe arg1 arg2 arg3
arg1 arg2 arg3

Go

package main

import (
	"fmt"
	"os"
)

func main() {

	args := os.Args[1:] // first value is program path
	fmt.Println(args)
}

output

❯ go run  examples/cli_args.go  arg1 arg2 arg3
[arg1 arg2 arg3]

🔶 Command-Line Flags

---

C#

using System;
using System.Linq;

class Program
{
  static void Main(string[] args)
  {
    if (args.Length > 0)
    {
      var flags = args
          .Select(x => x.Split('='))
          .ToDictionary(x => x[0], x => x[1]);

      foreach (var kv in flags)
        Console.Write($"{kv.Key}: {kv.Value}\n");
    }
  }
}

output

❯ cli_flags.exe default-user=adam  disable-log=true
default-user: adam
disable-log: true

Go

package main

import (
	"flag"
	"fmt"
)

func main() {

	strPtr := flag.String("default-user", "guest", "default username")
	numPtr := flag.Int("log-level", 2, "log level")
	var boolPtr bool
	flag.BoolVar(&boolPtr, "disable-log", false, "disable logs")

	flag.Parse()

	fmt.Println("default-user:", *strPtr)
	fmt.Println("log-level:", *numPtr)
	fmt.Println("disable-log:", *&boolPtr)
}

output

❯ go run  examples/cli_flags.go -default-user=adam  -disable-log=true
default-user: adam
log-level: 2
disable-log: true

🔶 Testing

---

C#

There are many unit-testing frameworks to test C# code such as NUnit, XUnit, and MSTest.
The following example uses NUnit:

using NUnit.Framework;

class Example
{
  public static int Sum(int a, int b) => a + b;
}

class ExampleTests
{
  [TestCase(2, 4, ExpectedResult = 6, TestName = "2+4")]
  [TestCase(-1, 1, ExpectedResult = 0, TestName = "-1+1")]
  [TestCase(-5, 3, ExpectedResult = -2, TestName = "-5+3")]
  public int SumTest(int a, int b)
  {
    return Example.Sum(a, b);
  }
}

Go

Go's standard library has the following testing packages:

• testing: provides support for automated testing.
• quick: has functions to help with black box testing.
• iotest: provides Reader and Writer implementations useful for testing.
• httptest: provides utilities for HTTP testing.

package example

import (
	"fmt"
	"testing"
)

func sum(a, b int) int {
	return a + b
}

func TestSum(t *testing.T) {
	data := []struct {
		a, b, sum int
	}{
		{2, 4, 6},
		{-1, 1, 0},
		{-5, 3, -2},
	}

	for _, tt := range data {
		name := fmt.Sprintf("%d+%d", tt.a, tt.b)
		t.Run(name, func(t *testing.T) {
			res := sum(tt.a, tt.b)
			if res != tt.sum {
				t.Errorf("expected %d, actual %d", tt.sum, res)
			}
		})
	}
}

output (The test file should have a name ending in _test.go)

❯ go test -v examples\example_test.go
=== RUN   TestSum
=== RUN   TestSum/2+4
=== RUN   TestSum/-1+1
=== RUN   TestSum/-5+3
--- PASS: TestSum (0.00s)
    --- PASS: TestSum/2+4 (0.00s)
    --- PASS: TestSum/-1+1 (0.00s)
    --- PASS: TestSum/-5+3 (0.00s)
PASS
ok      command-line-arguments  0.414s