Go - math.MaxInt64 and Type Inference Error

Question

I've been working on metaprogramming involving packages and I've been running into the error constant 9223372036854775807 overflows int whenever math.MaxInt64 and math.MaxUint64 show up.

I've isolated it into two cases:

Valid

var a int64 = math.MaxInt64
b := interface{}(int64(math.MaxInt64))

Not Valid

a := math.MaxInt64
b := interface{}(math.MaxInt64)

https://play.golang.org/p/U1QDmFbV29

It seems like that Go doesn't do correct type inference.

Is this a bug or expected behavior? And if expect, does anyone know why?

Answer 1

math.MaxInt64 is an Untyped Constant. Numeric constants represent values of arbitrary precision and do not overflow. When you assign this to a variable it needs to be converted to a numeric type, and if none is specified, int is used by default.

Since the int type in Go represents the native size for your architecture, this will overflow on systems with 32 bit ints.