How does type reflection for implicit types work?

As far as I know, go is statically typed and usually does not perform implicit type conversion. Therefore, constants without an explicit type declaration are subject to requirements on first use.

So, in the code snippet below, I wantnto befloat64, because that's whatmath.sinexpects. But when printing out the reflected type, I seeint.

package main import ( "fmt" "math" "reflect" ) func main() { const n = 5000 // No explict type // fmt.Println(reflect.TypeOf(n)) // this would print "int" fmt.Println(math.Sin(n)) // math.Sin expects a float64 fmt.Println(reflect.TypeOf(n)) // print "int" }

What exactly happened here?nIs there actually an implicit int type? Or reflection won't show actual type cases like this? I don't thinkmath.sinis typecasting its argument because the compiler will throw an error if I specify an explicit type.

Correct answer

[The type of untyped constant] depends on the requirements for first use.

This is where you got it wrong. A type is selected independently for each use.

math.Sin requires a float64 argument, so the compiler must select float64 here.

reflect.TypeOf takes an interface{} parameter, so the compiler is free to choose any numeric type (since they all implement the empty interface). The default integer type is selected here: int.

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