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P0919R3 Heterogeneous lookup for unordered containers #2479

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merged 3 commits into from Nov 26, 2018
Merged

P0919R3 Heterogeneous lookup for unordered containers #2479

merged 3 commits into from Nov 26, 2018

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burblebee
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Fixes #2433.

@jensmaurer jensmaurer changed the title Motions 2018 11 lwg 27 P0919R3 Heterogeneous lookup for unordered containers Nov 16, 2018
@jensmaurer jensmaurer added this to the post-2018-11 milestone Nov 16, 2018
burblebee
burblebee commented Nov 23, 2018
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source/containers.tex Outdated Show resolved Hide resolved
@burblebee burblebee added the changes requested Changes to the wording or approach have been requested and not yet applied. label Nov 23, 2018
@cpplearner
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The following uses of Pred should probably be changed to use key_equal (or "key equality predicate").

draft/source/containers.tex

Line 2168 in c1140dc

container. The container's object of type \tcode{Pred} ---

draft/source/containers.tex

Lines 2351 to 2353 in c1140dc

& \requires\ \tcode{Pred} is \oldconcept{CopyConstructible}.\br
\tcode{Pred} shall be a binary predicate that takes two arguments
of type \tcode{Key}. \tcode{Pred} is an equivalence relation.%

draft/source/containers.tex

Line 2939 in c1140dc

unless the \tcode{Pred} function object has

draft/source/containers.tex

Line 2944 in c1140dc

of the partition into equivalent-key groups produced by \tcode{Pred}.

draft/source/containers.tex

Line 3023 in c1140dc

\tcode{Pred} object (if any).

draft/source/containers.tex

Line 3034 in c1140dc

\tcode{Hash} or \tcode{Pred} object (if any).

draft/source/containers.tex

Line 7619 in c1140dc

is_nothrow_move_assignable_v<Pred>);

draft/source/containers.tex

Line 7677 in c1140dc

is_nothrow_swappable_v<Pred>);

draft/source/containers.tex

Line 8177 in c1140dc

is_nothrow_move_assignable_v<Pred>);

draft/source/containers.tex

Line 8218 in c1140dc

is_nothrow_swappable_v<Pred>);

draft/source/containers.tex

Line 8518 in c1140dc

is_nothrow_move_assignable_v<Pred>);

draft/source/containers.tex

Line 8557 in c1140dc

is_nothrow_swappable_v<Pred>);

draft/source/containers.tex

Line 8819 in c1140dc

is_nothrow_move_assignable_v<Pred>);

draft/source/containers.tex

Line 8858 in c1140dc

is_nothrow_swappable_v<Pred>);

@zygoloid
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@cpplearner I think you might be right, but it's not clear to me that that's an editorial change. In particular, the behavior of unordered containers with a hasher that has a transparent_key_equal and whose Pred is equal_to<Key> (which is the only possibility where it can be different from the transparent_key_equal type) seems highly underspecified to me. (Is the specified Pred entirely ignored, or sometimes still used? What happens if operator== is inconsistent with the "transparent" key equality functor? How does eg unordered_set<std::string, hash_by_lowercased_contents> behave?)

Can you ask to get a library issue opened to replace Pred with key_equal in all the relevant places?

@zygoloid zygoloid merged commit d6700cc into master Nov 26, 2018
@jensmaurer jensmaurer deleted the motions-2018-11-lwg-27 branch October 19, 2019 20:05
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@burblebee @cpplearner @zygoloid @jensmaurer