Declaring variables

Variables are immutable by default at the time of their declaration. To mark a variable as mutable, use the mut modifier.

A variable is declared with the val keyword:

val stdio = use("std/stdio")

pub fn main() void = trust {
    val x = 10
    stdio.print("{d}\n", {x})
}

The example uses the standard-library wrapper stdio.print, which delegates to the @print intrinsic. Unused variables are a compile-time error in Spectre.

To give a variable an explicit type:

val x: i32 = 10

This example asserts to the compiler that the value is a 32-bit signed integer.

Mutable values are declared with mut:

val x: mut i32 = 10

The mut modifier is part of the type, which makes the mutability of a value explicit when it is passed between functions.

A variable that is marked mutable but is never mutated is a compile-time error.