Variables

Variables are declared using the let keyword. All variables are constant by default, so mutability is specified with the mut keyword, that follows let. This keyword can also be used in the context of function parameter definitions. Type annotations are also a feature of the language, though are not recommended unless necessary for simplicity of reading, as the compiler can deduce it. The exception is when you declare a variable without assigning an initial expression to it, or when declaring function parameters.

let x: i64 = 21; // the type annotation here is not necessary, as its deducable from the RHS

let mut x: i64 = 21; // this variable can be mutated later on in the programs runtime

X supports both global and local variables. They are assigned in the same way.

Global variable names must be unique. However, for local variables, they do not need to be, but the compiler will complain in some instances. It is recommended that variable declarations are overwritten only in the case of tuple destructuring or when specifying a variable as unused, i.e. ‘_’.

fn swap(mut a: i64*, mut b: i64*) -> void {
    let temp= *a;
    *a = *b;
    *b = temp;
}

fn main() -> void {
    let mut a = 2;
    let mut b = 3;
    swap(&a, &b);
    io::println(a);
    io::println(b);
    return;
}