2 things:
1. plus() returns interface{}.
"%T" prints underlying dynamic type of interface{} value, but static type
of returned value of plus is interface{}
You can assign any type to interface{} without a cast by definition (see
e.g. https://www.programming-books.io/essential/go/a-90100072-empty-interface)
What it means is this is valid in Go:
var v interface{}
v = 5 // no cast needed
v = "foo" // no cast needed
interface{} is Go's version of dynamic type. It wraps any type as a tuple
(type, value).
2. Let's expand plus() function:
func plus(a, b interface{}) interface{} {
aInt := a.(myInt) // type: myInt
bInt := b.(myInt) // type: myInt
res := aInt + bInt // type: myInt
var ires interface{} = res; // no cast needed, see above
return ires
}
Hope this clarifies the typing.
Aside: if you come from C++, aliasing interface{} as any might feel
comfortable, but that's not a good Go style.
On Saturday, February 17, 2018 at 9:03:58 PM UTC-8, Bill Wood wrote:
>
> HI, Go newbie here... not sure if this is a dumb question or not :)
>
> I have a simple program:
>
> package main
>
> import "fmt"
>
> type any interface{}
> type myInt int
>
> func plus(a, b any) any { return a.(myInt) + b.(myInt) }
>
> func main() {
> s := plus(myInt(3), myInt(2))
> fmt.Printf("%v, %T\n", s, s)
> }
>
>
> Output:
>
> 5, main.myInt
>
>
> Why does func plus return a myInt? Why isn't a cast needed, ie:
>
> func plus(a, b any) any { return myInt(a.(myInt) + b.(myInt)) }
>
>
> Thanks!
>
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