Can't overload = for a generic.

[kayabaNerve]

For a Generic defined as:

type Generic*[T] = object
    value: T

There are four potential definitions of =.

proc `=`(x: var Generic, y: Generic) #Doesn't match the needed signature.

proc `=`(x: var Generic[int], y: Generic[int]) #Doesn't match the needed signature and violates the purpose of Generics.

proc `=`(x: var Generic[X], y: Generic[X]) #X (not T as T is Generic[X]) is undefined.

proc `=`[T](x: var Generic[T], y: Generic[T]) #Compiles, but is never run.

Is this a feature that has yet to be implemented/is broken or will Nim not support Generic = overloading?

[Araq]

proc =[T](x: var Generic[T], y: Generic[T]) #Compiles, but is never run.

That's currently the only supported syntax and it is invoked, I have plenty of tests that prove it. :P

[mratsim]

I wouldn't trust assignment overloading.

Quoting @Araq in #6348 (comment)

Assignment overloading is unusable for everything right now.

My experiments to introduce a custom copy-on-write also failed utterly due to it: #6786

[kayabaNerve]

I'm obviously not someone who knows the Nim compiler as well as @Araq, but it hasn't been invoked on my tests in devel.

My guess is [T] is being defined as Generic[X] so it has to match Generic[Generic[X]], which it doesn't. For whatever reason it isn't working, do you have an test that explicitly tests overloading for generics?

[kayabaNerve]

Here's the exact code I'm testing with a devel compiler from November 11th.

type Generic[T] = object
    value: T

proc `=`[T](x: var Generic[T], y: Generic[T]) = #Compiles, but is never run.
    echo 1

var t: Generic[int]
t = Generic[int](value: 5)
echo t.value

1 is never printed; the value is set to 5.

[kayabaNerve]

https://pastebin.com/fnndzshY

Those are three different methods of Generic creation. One uses alloc inside a function. One doesn't alloc anything. One uses alloc outside of a function. Only the one that uses alloc inside a function triggers.