Variables

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

Binding	Mutability	Description
let	Immutable	Cannot be reassigned after initialization
var	Mutable	Can be reassigned at any time

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.

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: 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

Topic	Description
Immutable Variables (let)	The default binding and why to prefer it
Mutable Variables (var)	Reassignment and compound assignment
Mutability of Structs	How let and var govern field changes

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

See Also

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