https://go.googlesource.com/proposal/+/refs/heads/master/design/go2draft-type-parameters.md#pointer-method-example
has this example:
// Setter2 is a type constraint that requires that the type
// implement a Set method that sets the value from a string,
// and also requires that the type be a pointer to its type parameter.
type Setter2(type B) interface {
Set(string)
type *B
}
// FromStrings2 takes a slice of strings and returns a slice of T,
// calling the Set method to set each returned value.
//
// We use two different type parameters so that we can return
// a slice of type T but call methods on *T aka PT.
// The Setter2 constraint ensures that PT is a pointer to T.
func FromStrings2(type T interface{}, PT Setter2(T))(s []string) []T {
result := make([]T, len(s))
for i, v := range s {
// The type of &result[i] is *T which is in the type list
// of Setter2, so we can convert it to PT.
p := PT(&result[i])
// PT has a Set method.
p.Set(v)
}
return result
}
I wonder if it might be worthwhile to allow specifying pointer methods in
interfaces, so that we could write instead
type Setter3 interface {
// For type T to implement Setter3, *T must have a Set method.
* Set(string)
}
func FromStrings3(type T Setter3(T))(s []string) []T {
result := make([]T, len(s))
for i, v := range s {
result[i].Set(v)
}
}
This is simpler in two ways: FromStrings3 only needs one interface
constraint, and it does not need to convert &result[i] to a type parameter,
but can call result[i].Set(v) directly.
I imagine interfaces containing pointer methods should be used only as
constraints on type parameters, not as normal interfaces.
I have no idea if such cases arise often enough to make this idea
worthwhile.
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