P1716R3 ranges compare algorithm are over-constrained #3450
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Looks good. Asked LWG about order of template parameters: http://lists.isocpp.org/lib/2019/11/14279.php
| class Proj1 = identity, class Proj2 = identity, | ||
| indirect_relation<projected<I1, Proj1>, | ||
| projected<I2, Proj2>> Pred = ranges::equal_to> | ||
| class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity> |
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This changes the relative order of Proj1, Proj2, Pred template parameters to be Pred, Proj1, Proj2 instead. I couldn't find a mention in the prose text section of the paper that this was intended. Having deducible template parameters in the same order as the function parameters seems reasonable, though.
| @@ -846,11 +846,13 @@ | |||
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| namespace ranges { | |||
| template<forward_iterator I, sentinel_for<I> S, class Proj = identity, | |||
| indirect_relation<projected<I, Proj>> Pred = ranges::equal_to> | |||
| indirect_binary_predicate<projected<I, Proj>, | |||
| projected<I, Proj>> Pred = ranges::equal_to> | |||
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I'm confused. Here, "Proj" still comes first in the template parameters. This is oddly inconsistent. (There might be arcane cases where users might want to specify explicit template argument lists.)
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(There might be arcane cases where users might want to specify explicit template argument lists.)
The number and order of deducible template parameters for algorithm declarations are unspecified, except where explicitly stated otherwise.
[ Note: Consequently, the algorithms may not be called with explicitly-specified template argument lists. — end note ]
| indirect_relation<projected<I1, Proj1>, | ||
| projected<I2, Proj2>> Pred = ranges::equal_to> | ||
| class Pred = ranges::equal_to, class Proj1 = identity, class Proj2 = identity> | ||
| requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2> |
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Again, the order of template parameters is changed. Note that indirectly_comparable also takes Pred, Proj1, Proj2 (but we take Proj1, Proj2, Pred). Go figure.
| requires indirectly_comparable<I1, I2, Pred, Proj1, Proj2> | ||
| sentinel_for<I2> S2, class Proj1 = identity, class Proj2 = identity, | ||
| indirect_equivalence_relation<projected<I1, Proj1>, | ||
| projected<I2, Proj2>> Pred = ranges::equal_to> |
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Here, we switch Pred, Proj1, Proj2 to Proj1, Proj2, Pred (i.e. the "other" order). This is seriously confusing.
Also fixes NB GB 183, US 267, US 306, and PL 312 (C++20 CD).
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Fixes #3409.
Fixes cplusplus/nbballot#181.
Fixes cplusplus/nbballot#263.
Fixes cplusplus/nbballot#302.
Fixes cplusplus/nbballot#308.
Fixes cplusplus/papers#482
Also fixes NB GB 183, US 267, US 306, and PL 312 (C++20 CD).