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Value assignment has the following syntax: (const|var) identifier[: type] = value.

  • const indicates that identifier is a constant that stores an immutable value.
  • var indicates that identifier is a variable that stores a mutable value.
  • : type is a type annotation for identifier, and may be omitted if the data type of value can be inferred.
const constant: i32 = 5; // signed 32-bit constant
var variable: u32 = 5000; // unsigned 32-bit variable

// @as performs an explicit type coercion
const inferred_constant = @as(i32, 5);
var inferred_variable = @as(u32, 5000);

Constants and variables must have a value. If no known value can be given, the undefined value, which coerces to any type, may be used as long as a type annotation is provided.

const a: i32 = undefined;
var b: u32 = undefined;

Where possible, const values are preferred over var values.