Typed vs. untyped constants

As explained in type casting, Go doesn’t perform implicit type casts between integer types.

Untyped constants make using integer types easier:

main.go

	const untypedNumber = 345

	// if this was a variable declaration, untypedNumber would have its type
	// inferred as int.
	// since it's a const, it remains untyped until it's e.g. assigned to a variable
	var i int = untypedNumber      // no need to cast to int
	var u16 uint16 = untypedNumber // no need to cast to uint16
	var f float64 = untypedNumber  // no need to cast to float64

	// incompatible assignments are detected by the compiler
	// 345 is too big to fit in int8 and compiler detects that
	var b int8 = untypedNumber

Output:

# test
./main.go:17:6: constant 345 overflows int8
exit status 2

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