On Mon, Dec 19, 2022 at 8:31 PM Red Daly <redd...@gmail.com> wrote:
> Methods cannot take type arguments, so I find myself writing `func Foo(o
> Object) {...}` instead of `func (o Object) Foo()` in cases where Foo needs
> a type parameter.
>
> I would like some type of pseudo-method in Go similar to Kotlin's
> extension methods. Made up syntax:
>
> ```go
> package foo
>
> func (o Object) #Foo[T any]() { /* ... */ } // Foo is a pseudo method of
> Object
>
> func main() {
> obj := Object{}
> obj#Foo() // use # to differentiate from regular methods, or use .
> }
> ```
> or something more clever.
>
> I expect a lot of the time people use methods for syntactic reasons, not
> so those methods can be used to implement an interface. Methods appear in
> godoc along with the type, get better tab completion than functions, etc.
> I'm not proposing these pseudo-methods be used in any way to implement
> interfaces.
>
> This may have already been discussed. There have been rejected proposals
> for adding methods to types defined elsewhere (
> https://github.com/golang/go/issues/37742 and
> https://github.com/golang/go/issues/21401). However, I can't find a
> proposal that proposes the Kotlin approach to "extension methods," which is
> largely syntax sugar that allows `fun koo(k Kobject): void` to be called
> like `k.koo()` by the programmer (rather than `koo(k)`) so long as `koo` is
> statically resolved where such `k.koo` calls appear. Is there such a
> proposal?
>
There are (at least) two:
https://github.com/golang/go/issues/56283
https://github.com/golang/go/issues/56242
It's not *exactly* what you describe, but I believe it's close enough.
>
> This feature would be useful for defining these pseudo-methods on types
> within a package or on types from other packages. Using a pseudo-receiver
> type that's defined in another package raises some questions about how to
> use the pseudo-method without surprising/confusing readers. Most
> prominently for writing method-like generic functions.
>
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