proposal: spec: automatically instantiate generic field types that are already concrete types

[phenpessoa]

Currently, when you have a generic field in a struct that has a generic, but already concrete, type, to instantiate that struct you need to explicitly tell the compiler the type.

Example:

type Foo struct {
	Field Field[int]
}

type Field[T any] struct {
	Val T
}

func Bar() Foo {
	return Foo{
		Field: Field[int]{
			Val: 10,
		},
	}
}

I find Field: Field[int]{... to be redudant, because that Field can not be of any type but an int.

I propose that this would become possible:

type Foo struct {
	Field Field[int]
}

type Field[T any] struct {
	Val T
}

func Bar() Foo {
	return Foo{
		Field: Field{
			Val: 10,
		},
	}
}

Currently, this error out as cannot use generic type Field[T any] without instantiation.

[seankhliao]

Duplicate of #50285