P0458R2 Checking for existence of an element in associative containers #2163
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jensmaurer
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| \tcode{con\-tains(ke)} & | ||
| \tcode{bool} & | ||
| equivalent to \tcode{a_tran.find(ke) != a_tran.end()} & | ||
| logarithmic \\ \rowsep |
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I think we can do without the a_tran changes; since a_tran is a restriction of "b" and the semantics don't differ, we should be good. (The semantics of find() do differ, though, but that's hidden behind the function call.)
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So should it b b.contains(ke)? Because otherwise we're only defining what happens if you call contains with the key type, and the transparent versions accept anything that can be compared to the key.
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Ah, that's the point.
Tell me more: We have these template <class K> overloads all over the place; does that mean they're not active for non-transparent comparators?
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But b.contains(ke) doesn't necessarily work, it only works if b has a transparent comparison function, in which case we'd use a_tran.
I think we need both rows. The b row is always valid, the a_tran row (which isn't restricted to arguments convertible to key_type) is only conditionally valid.
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does that mean they're not active for non-transparent comparators?
Yes, see [associative.reqmts] p14.
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Ah, so we need to edit p14 to add contains!
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After informing LWG of my intention, I've added contains to p14 in a Fixup push to the branch.
source/containers.tex
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| @@ -7536,6 +7567,7 @@ | |||
| iterator find(const key_type& k); | |||
| const_iterator find(const key_type& k) const; | |||
| size_type count(const key_type& k) const; | |||
| bool contains(const key_type& x) const; | |||
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The key_type parameter name is called "k" in the vicinity. We should stay consistent.
source/containers.tex
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| @@ -8064,6 +8096,7 @@ | |||
| iterator find(const key_type& k); | |||
| const_iterator find(const key_type& k) const; | |||
| size_type count(const key_type& k) const; | |||
| bool contains(const key_type& x) const; | |||
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The key_type parameter name is called "k" in the vicinity. We should stay consistent.
source/containers.tex
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| @@ -8390,6 +8423,7 @@ | |||
| iterator find(const key_type& k); | |||
| const_iterator find(const key_type& k) const; | |||
| size_type count(const key_type& k) const; | |||
| bool contains(const key_type& x) const; | |||
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The key_type parameter name is called "k" in the vicinity. We should stay consistent.
source/containers.tex
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| @@ -8678,6 +8712,7 @@ | |||
| iterator find(const key_type& k); | |||
| const_iterator find(const key_type& k) const; | |||
| size_type count(const key_type& k) const; | |||
| bool contains(const key_type& x) const; | |||
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The key_type parameter name is called "k" in the vicinity. We should stay consistent.
[associative.reqmts] Add "contains" to the list of member function templates that do not participate in overload resolution unless the comparator is transparent, as agreed on the lib reflector.
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Fixes #2133