8000 Type parameters in `new Mapping<TypeA, TypeB>`/ `new Listing<Type>` are not checked · Issue #405 · apple/pkl · GitHub
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Type parameters in new Mapping<TypeA, TypeB>/ new Listing<Type> are not checked #405

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bioball opened this issue Apr 5, 2024 · 3 comments · Fixed by #628
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Type parameters in new Mapping<TypeA, TypeB>/ new Listing<Type> are not checked #405

bioball opened this issue Apr 5, 2024 · 3 comments · Fixed by #628
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@bioball
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bioball commented Apr 5, 2024 •
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This does not throw, but should:

foo = new Listing<Int> {
  "hello"
}

In the below, both types should be checked:

foo: Listing<Int(isEven)> = new Listing<Int(this > 5)> { 1; 2; 3 }

The check should not follow when amended.

This is fine:

foo: new Listing<Int> { 1; 2; 3 }

bar = (foo) { "hello" }

This should probably be fine too:

foo = new Listing<Int> { 1 } { "hello" }
@bioball bioball mentioned this issue Apr 5, 2024
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@bioball bioball added the bug Something isn't working label Apr 5, 2024
@odenix
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odenix commented Apr 12, 2024 •
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A pragmatic solution would be to allow x: Listing<A> = new Listing {...} but not x = new Listing<A> {...}. This would reflect the (current) reality that generics aren't reified. It would also encourage users to do the right thing and put type annotations on their properties. It might even allow to phase out new Type {...} in favor of (Type) {...}, which in my view is a nicer literal syntax.

@holzensp
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That's less simple than you might think. The generic informs the default / IDE type checking. It's a common pattern to define Listings inline to produce something of a very different type, such as new Listing<String> { ... }.join(", ") to produce a String.

@odenix
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odenix commented Apr 17, 2024 •
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Dealing with generics is never simple. Regarding your concrete arguments, Listing.join is defined for all Listings, not just Listing<String>. And IDEs could still try to infer the element type from the given elements. The default sounds like a bigger problem, but maybe there is an acceptable solution.

@holzensp holzensp mentioned this issue Apr 29, 2024
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@bioball bioball mentioned this issue Jun 10, 2024
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This was referenced Aug 15, 2024
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Overhaul typechecks for Mapping/Listing bioball/pkl
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