Refresher.md

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Must Refer

swift apple documentation

swift lang documentation

swift tutorials point

iOS Basic Info

• iPhone OS(first name)
• Unix based
• first os with muti touch GUI,in their words a phone that runs macOS
• Latest Version - 12.2
• Privacy oriented

Development Languages

• swift Curent version: swift 5.0 open source modern and better performance than objective c
• objective c (header(.h) and implementation (.m) files ) Programming language for NeXTSTEP OS
• c and c++ (limited)

Swift Language

Swift includes modern features like type inference, optionals, and closures, which make the syntax concise yet expressive. Swift ensures your code is fast and efficient, while its memory safety and native error handling make the language safe by design. Writing Swift code is interactive and fun in Swift Playgrounds, playgrounds in Xcode, and REPL.

Constants and Variables

Variables are nothing but reserved memory locations to store values. This means that when you create a variable, you reserve some space in memory

let : constant
var: variable

• Type Annotations Telling the type of a variable or constant

var name: String

• Type Inference The ability of Swift's compiler to figure out what kind of data type should be assigned to each of your variables and constants, so you don't have to explicitly state it.

var name = "Swift"

• Type Aliases

  Type aliases define an alternative name for an existing type. You define type aliases with the typealias keyword.

• Type Coversion

  SomeType(ofInitialValue) is the default way to call the initializer of a Swift type and pass in an initial value.

• Typecasting

  Type casting is a way to check the type of an instance, or to treat that instance as a different superclass or subclass from somewhere else in its own class hierarchy.

  Type casting in Swift is implemented with the is and as operators. These two operators provide a simple and expressive way to check the type of a value or cast a value to a different type.

• Naming Constant and variable names can’t contain whitespace characters, mathematical symbols, arrows, private-use Unicode scalar values, or line- and box-drawing characters.

  Nor can they begin with a number, although numbers may be included elsewhere within the name

Data Types

Based on the data type of a variable, the operating system allocates memory and decides what can be stored in the reserved memory.

Built-in Data Types

In Swift Data types are internally implemented as structs.

The swift standard library contains Int,Double,String,Array,Dictionary as structs,

Swift offers the programmer a rich assortment of built-in as well as user-defined data types. The following types of basic data types are most frequently when declaring variables −

• Int or UInt − This is used for whole numbers. More specifically, you can use Int32, Int64 to define 32 or 64 bit signed integer, whereas UInt32 or UInt64 to define 32 or 64 bit unsigned integer variables. For example, 42 and -23.

• Float − This is used to represent a 32-bit floating-point number and numbers with smaller decimal points. For example, 3.14159, 0.1, and -273.158.

• Double − This is used to represent a 64-bit floating-point number and used when floating-point values must be very large. For example, 3.14159, 0.1, and -273.158.

• Bool − This represents a Boolean value which is either true or false.

• String − This is an ordered collection of characters. For example, "Hello, World!"

• Character − This is a single-character string literal. For example, "C"

• Optional − This represents a variable that can hold either a value or no value.

• Tuples − This is used to group multiple values in single Compound Value.

  Few important points related to Integer types −

  • On a 32-bit platform, Int is the same size as Int32.

  • On a 64-bit platform, Int is the same size as Int64.

  • On a 32-bit platform, UInt is the same size as UInt32.

  • On a 64-bit platform, UInt is the same size as UInt64.

  • Int8, Int16, Int32, Int64 can be used to represent 8 Bit, 16 Bit, 32 Bit, and 64 Bit forms of signed integer.

  • UInt8, UInt16, UInt32, and UInt64 can be used to represent 8 Bit, 16 Bit, 32 Bit and 64 Bit forms of unsigned integer.

Tuples

Tuples group multiple values into a single compound value. The values within a tuple can be of any type and don’t have to be of the same type as each other.

1.  let http404Error = (404, "Not Found")
2.  // http404Error is of type (Int, String), and equals (404, "Not Found")

Tuples are useful for temporary groups of related values. They’re not suited to the creation of complex data structures.

Optionals

You use optionals in situations where a value may be absent. An optional represents two possibilities: Either there is a value, and you can unwrap the optional to access that value, or there isn’t a value at all.

Optional Binding

You use optional binding to find out whether an optional contains a value, and if so, to make that value available as a temporary constant or variable. Optional binding can be used with if and while statements to check for a value inside an optional, and to extract that value into a constant or variable, as part of a single action

if let constantName = someOptional {
  statements
  }

Implicitly Unwrapped Optionals

You write an implicitly unwrapped optional by placing an exclamation mark (String!) rather than a question mark (String?) after the type that you want to make optional.

Implicitly unwrapped optionals are useful when an optional’s value is confirmed to exist immediately after the optional is first defined and can definitely be assumed to exist at every point thereafter. The primary use of implicitly unwrapped optionals in Swift is during class initialization.

Optional Chaining

The process of querying, calling properties, subscripts and methods on an optional that may be 'nil' is defined as optional chaining. Optional chaining return two values −

Optional Chaining is used as an alternative to Forced Unwrapping

• if the optional contains a 'value' then calling its related property, methods and subscripts returns values

• if the optional contains a 'nil' value all its its related property, methods and subscripts returns nil

Optional chaining fails gracefully when the optional is 'nil'.

Error Handling

You use error handling to respond to error conditions your program may encounter during execution.

In contrast to optionals, which can use the presence or absence of a value to communicate success or failure of a function, error handling allows you to determine the underlying cause of failure, and, if necessary, propagate the error to another part of your program.

When a function encounters an error condition, it throws an error. That function’s caller can then catch the error and respond appropriately.

  func canThrowAnError() throws {
  // this function may or may not throw an error
  }

Swift automatically propagates errors out of their current scope until they’re handled by a catch clause.

  do {
  try canThrowAnError()
  // no error was thrown
 } catch {
  // an error was thrown
  }

A do statement creates a new containing scope, which allows errors to be propagated to one or more catch clauses.

Assertions and Preconditions

Assertions and preconditions are checks that happen at runtime. You use them to make sure an essential condition is satisfied before executing any further code. If the Boolean condition in the assertion or precondition evaluates to true, code execution continues as usual. If the condition evaluates to false, the current state of the program is invalid; code execution ends, and your app is terminated.

The difference between assertions and preconditions is in when they’re checked: Assertions are checked only in debug builds, but preconditions are checked in both debug and production builds.