[Static extensions] Can static extensions declare constructors with prefixed names?

The proposal for adding constructors to static extensions is currently (I believe) in a somewhat inconsistent state with respect to declaring constructors in extensions for which the on-declaration is a prefixed name. The text possibly implies that it may be possible to declare such a constructor using a prefixed name, however, I believe that the syntax does not yet support such a declaration, and also the text around invocations I believe would need some modification to account for this. Consider the following examples:

import "foo.dart" as f; // foo.dart declares a class named C and a class named f
import "foo.dart" show D; // foo.dart also declares a class named C

extension E1 on f.C {
  f.C.name(); // Is this a valid declaration of a constructor named `C.name`?
}

extension E2 on f.C {
  C.name(); // Is this a valid declaration of a constructor named `C.name`?
}

extension E2 on f.f {
  f.f(); // Is this a valid declaration of a constructor named `f.f`?  Or of a constructor named `f.new`?
}

extension E4 on D {
  f.D.name(); // Is this a valid declaration of a constructor named `D.name`?
}

What do we intend to support here?

cc @dart-lang/language-team

I'd say "none of the above", and only support new nameless constructor syntax, new(), new.id(), const() or const.id().

That should avoid any issue.

Otherwise I'd probably go with E2. The name of the class in the constructor declaration is not a scope lookup, it's "the same name as the surrounding class".
The name of the class being extended is C.
Or maybe it isn't, you can make an extension on a public alias of a privately named class.

The only way to win is not to play. Just don't write a name

We talked about this in the meeting, we will do what Lasse proposes above.

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[Static extensions] Can static extensions declare constructors with prefixed names? #4681

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[Static extensions] Can static extensions declare constructors with prefixed names? #4681

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lrhn commented on Apr 15, 2026

leafpetersen commented on Apr 15, 2026

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