Untyped numeric constants with no limits

Constants may be typed or untyped.

const a uint = 17
const b = 55

An untyped constant has no limits. When it’s used in a context that requires a type, a type will be inferred and a limit applied.

const big = 10000000000  // Ok, even though it's too big for an int.
const bigger = big * 100 // Still ok.
var i int = big / 100    // No problem: the new result fits in an int.

// Compile time error: "constant 10000000000 overflows int"
var j int = big

The inferred type is determined by the syntax of the value:

• 123 gets type int, and
• 123.4 becomes a float64.

The other possibilities are rune (alias for int32) and complex128.

Enumerations

Go does not have enumerated types. Instead, you can use the special name iota in a single const declaration to get a series of increasing values. When an initialization expression is omitted for a const, it reuses the preceding expression.

const (
	red = iota // red == 0
	blue       // blue == 1
	green      // green == 2
)

See 4 iota enum examples for further examples.