[PATCH] D128750: [c++20] Implement P2113R0: Changes to the Partial Ordering of Constrained Functions

Wed Jul 6 16:25:14 PDT 2022

ychen added a comment.

In D128750#3627085 <https://reviews.llvm.org/D128750#3627085>, @royjacobson wrote:

> Thanks for working on this! I like the approach, but two comments:

Thanks for the review.

> I would like more tests for the different forms of template argument deduction. Some suggestions for things to test: template template arguments, 'auto' in abbreviated function templates, argument packs, non-type template parameters. We should at least test that we find the more constrained function when the parameters are equal.

Sure, will do.

> I'm also a bit concerned that we're deviating from the standard here w.r.t. to the 'reordering' checks for reversed candidates. I support this - I think your version makes more sense than what the standard says to do here - but if someone could check with the committee (I don't have reflector access myself) that we're not breaking some important use case by doing it this way, I think it's a good idea.

Yeah, I found it kinda hard to implement the `reordering` aspect efficiently. My understanding of the `reordering` aspect is for finding an intuitive order of template parameters that makes sense for the following constraints tie breaker. Hi @hubert.reinterpretcast, could you please shed some light on the intended implementation for https://eel.is/c++draft/temp.func.order#6.2.1.2? I'm a little hesitant to use an exhaustive approach to find the template parameter order for constraints comparison. Does using deducing order sound reason to you? Thanks.

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