Variables

A variable binds a name to a value. Every binding is either immutable or mutable, chosen by the keyword that introduces it:

let answer = 42;   // immutable
var counter = 0;   // mutable
counter += 1;      // OK

Immutability is the default: prefer let, and reach for var only when a value genuinely needs to change. Function parameters follow the same rule — immutable unless declared var (see Mutable Parameters).

Type Inference and Annotations

When a binding has an initializer, the compiler infers its type. Add an explicit : Type annotation to choose a type other than the inferred one — a wider integer, say — or to declare a variable whose type cannot be inferred:

let pi = 3.14159;            // inferred float64
let name: Slice<char8> = "Rux";   // explicit annotation
var total: int64 = 0;        // explicit — wider than the default int

A variable's type is fixed once it is declared. Because Rux performs no implicit conversions, assigning a value of a different type is a compile-time error; convert explicitly with an as cast.

Topics in This Chapter

For named values computed at compile time, use const instead.

See Also

• Constants — compile-time named values
• Type Casts — converting between types when assigning