First-class generic method / First-class polymorphism / Rank-N types

[be5invis]

Given that we have

private void GenericMethod<T, U>(T obj, U parm1)

Which we can use like so:

GenericMethod("test", 1);
GenericMethod(42, "hello world!");
GenericMethod(1.2345, "etc.");

... but it is impossible for now to do this:

public void AnotherMethod(Action<???> method) {
    method("test", 1);
    method(42, "hello world!");
    method(1.2345, "etc.");
}
//...
AnotherMethod(GenericMethod);

...without using reflection/dynamic tricks.

What if we have a forall?

public void AnotherMethod(forall<T, U>. Action<T, U> method) {
    method("test", 1);
    method(42, "hello world!");
    method(1.2345, "etc.");
}
//...
AnotherMethod(GenericMethod);

[orthoxerox]

See also #2212

[alrz]

You should be passing the containing object so that overload resolution takes place directly on the original method.

class A {   
  public void GenericMethod<T, U>(T obj, U parm1) {}
}

class B {
  public void AnotherMethod(A a) {
    a.GenericMethod("test", 1);
    a.GenericMethod(42, "hello world!");
    a.GenericMethod(1.2345, "etc.");
  } 
}

[be5invis]

@orthoxerox Higher-kind polymorphism is not higher-rank polymorphism.

[CyrusNajmabadi]

Closing this out. We're doing all language design now at dotnet/csharplang. If you're still interested in this idea let us know and we can migrate this over to a discussion in that repo. Thanks!