Expose the names of generated record constructors #6975
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Since we have a new name for the record, we have to make sure that the new record is also associated with a constructor. But we also can't associate it with the old constructor, since that won't be applied to any parameters. So we rename the constructor when renaming the record, and fortunately the type checker is smart enough to recognise that it doesn't have to come up with a *third* name for the constructor, so the parameters are correctly instantiated.
Why? The notation |
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Because of the different scoping (visibility) rules. You could use Foo.constructor to get at Foo's constructor even if it's named and unexported (e.g. Foo lives in a private module which is open public hiding its constructor). |
andreasabel
approved these changes
Apr 17, 2024
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Since this is still marked as a draft, I'm moving it to |
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This PR's gonna be too much of a pain to merge so I'm just gonna frankenstein a new one. |
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The keyword
constructorcan appear as the last token in a qualified name, as long as it's the only name part. SoFoo.constructor,Foo.Bar.constructorare both valid, butconstructorandFoo.constructor.barare still syntax errors.The
Foo.constructorsyntax is actual syntax. It looks like a name, but there's noconstructorname in the moduleFoo. That would be incorrect anyway, since the record module is parametrized by a value of the record type, but the constructor isn't; see #4189. Because of this, it's not possible to control the visibility ofFoo.constructor: if you want that, give the constructor an actual name.If the constructor has a declared name, the
Foo.constructorsyntax is also disabled, with an error message explaining that the declared name should be used instead.To resolve
Foo.constructor, we look upFooas an unambiguous record name, and then resolve to the actual name of the constructor, which is still kept internal. This means thatFoo.constructoris in scope as long asFoois, so this doesn't reintroduce #282. It also means that renaming the record will also "rename" the constructor, as expected.