On Sat, Jan 31, 2026 at 10:01 AM Kevin Chowski <[email protected]> wrote:
>
> Hi all, I read through the spec to look for the rules about this but I think
> this is a consequence of a couple different parts, so I'm reaching out here
> for some expert help. I'm also wondering if the current state of affairs is
> due to a hard limitation or simply because "no one has found time to work on
> it yet".
>
> Why doesn't type inference choose a named type when it is an obvious
> candidate, and could it be enhanced to do so without too much trouble? What I
> mean: https://play.golang.com/p/gWMOBr-rMgq
>
> (btw, if you're surprised to see `var myFunc MyFunc = f` works correctly in
> that above link, it's because there are special assignment rules for *some*
> unnamed types, but not all; to be clear, I understand none of these work for
> MyInt and I (believe I) know why it's a good thing:
> https://play.golang.com/p/iN0Tz5i480A)
>
> Staving off "why do you even want this?": I want to do (something like) this
> because I have a lisp implementation where you can register typesafe builtins
> from Go code, and I'm trying to emulate variable type parameters so that
> instead of calling CompileFunc1 for functions with 1 argument, CompileFunc2
> for those with 2, etc, I can just use some CompileFuncN and have the type
> inference magically sort out the right type for me :) So I do already have a
> relatively simple way to handle this and don't need a new workaround, but I
> want to understand why I can't do something else.
This line:
func WithTypeParameter[F MyFunc](f F) {}
says that WithTypeParameter requires a type argument that matches
MyFunc. There is only such type argument, namely MyFunc itself. That
seems useless, so I don't understand your goal. We could probably add
an inference rule saying that if the type of the argument is
assignable to the type parameter constraint (when the constraint is
not an interface type), then use the type parameter constraint. But
approximately zero real programs would use that, because approximately
zero real programs would use a type parameter that only accepts a
single type argument.
Ian
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