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IterableExtension sortedBy doesn't permit sorting by int without workaround #271

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trinarytree opened this issue Feb 22, 2023 · 5 comments · May be fixed by #315
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IterableExtension sortedBy doesn't permit sorting by int without workaround #271

trinarytree opened this issue Feb 22, 2023 · 5 comments · May be fixed by #315
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type-question A question about expected behavior or functionality

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@trinarytree
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import 'package:collection/collection.dart';

void main() {
  [2, 1].sortedBy((i) => i);
}

yields

Error: Inferred type argument 'int' doesn't conform to the bound
'Comparable<K>' of the type variable 'K' on 'IterableExtension|sortedBy'.

sorting by an int is a pretty important use case.
the problem seems to be that sortedBy insists that its generic param K extend Comparable<K>
and int doesn't extend Comparable<int>. rather, it extends Comparable<num>.

workaround:

  [2, 1].sortedBy<num>((i) => i);

the workaround doesn't seem like it should be the end of this story.
i feel like the first example should just work. perhaps one could see this as a problem with the type inference system,
as in, why can't it figure out that K perhaps should be bound to a super class (num) of the exact type (int)
returned by the keyOf function?
@natebosch natebosch added the type-question A question about expected behavior or functionality label Feb 23, 2023
@natebosch
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Closing as a duplicate of dart-lang/sdk#43763

I don't think there is anything we can do from the package side.

@eseidel
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eseidel commented Oct 10, 2023

I think simply documenting this in the sortedBy docs would go a long way. :)

@eseidel eseidel mentioned this issue Oct 10, 2023
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@natebosch
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I think simply documenting this in the sortedBy docs would go a long way

Why sortedBy but not isSortedby, binarySearchBy, lowerBoundBy, or sortBy?

@eseidel
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eseidel commented Oct 10, 2023

I think simply documenting this in the sortedBy docs would go a long way

Why sortedBy but not isSortedby, binarySearchBy, lowerBoundBy, or sortBy?

No good reason. Was mostly trying to avoid "perfect being the enemy of the good" by documenting the one method through which myself and two other colleagues had independently encountered this error. 🤣 Happy to see something more systemic, just was trying to be helpful. I've personally not used any of the 4 other methods, but I have no data to say which are more/less common.

@natebosch
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I think if we do decide to address this with a note in the doc comment we can easily enough make it a template and repeat it in each impacted method.

Once we hear back from the analyzer team on the feasibility for making the diagnostic more informative we can make a choice on landing the PR.

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docs: Add a warning about dart-lang/sdk#43763 to sortedBy eseidel/collection
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@eseidel @trinarytree @natebosch