variables.md

version	example_title
1.0.0	Variables

Variables

In V variables can be declared and initialized with the := operator. Variables can only be declared this way in V, this means all variables have an initial value. The type of a variable is inferred from the value on the right hand side. By default variables in V are immutable.

age := 23               // int
name := 'Alice'         // string
is_adult := age > 21    // bool

println(age_str)        // 23
println(name)           // Alice
println(is_adult)       // true

Note: Variables can only be defined in a function. There are no global variables and no global state in V.

To change the value of a variable, it needs to be mutable. This can be done using the mut keyword when declaring the variable. To assign a new value to a variable use =.

mut age := 20       // declare the mutable variable age and assign it to the value 20.
println(age)        // 20
age = 21            // assign a new value to age
println(age)        // 21

Leaving out the mut keyword here would result in an error because the value of an immutable variable cannot be changed.

fn main() {
    age = 20
    println(age)
}

The code above would result in an error during compilation because the variable age is not declared,

fn main() {
    mut age := 20       // we declare the mutable variable age and assign it to the value 20.
    println(age)        // 20
    age := 21           // ERROR
}

here age := 21 will result in another error while compiling because the variable age is already defined in the scope. It's very simple to remember, just declare value with := and assign value with =.

Like Go, You can also use _ for ignoring values when it is not needed. Usually used in multi return functions.

_ := "I don't need this value"
println(_) // ERROR: Cannot use `_` as value

Naming Rules

The following are the rules which should be kept in mind while naming variables.

• Name should not contain Uppercase letters like AlphaTest
• Use underscores as separators like hello_world
• Name should be descriptive as possible
• Name should not contain __
• Name should not contain any space
• If the name is longer than 11 then it must use _ as separator

These rules are from Snake_Case. V uses Snake Case and prefers it because it is more easy to read, write and understand.

Valid Names

boby
john_dads
myfamily_number

Invalid Names

IamNotValid
new Make