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erase_if
for flat_{,multi}set
is incorrectly specifiedSection: 24.6.11.6 [flat.set.erasure], 24.6.12.6 [flat.multiset.erasure] Status: C++23 Submitter: Tim Song Opened: 2023-02-09 Last modified: 2023-11-22
Priority: Not Prioritized
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Discussion:
The current specification of erase_if
for flat_{,multi}set
calls ranges::remove_if
on the set, which is obviously incorrect —
the set only present constant views of its elements.
[Issaquah 2023-02-09; LWG]
Move to Immediate for C++23
[2023-02-13 Approved at February 2023 meeting in Issaquah. Status changed: Immediate → WP.]
Proposed resolution:
This wording is relative to N4928.
Modify 24.6.11.6 [flat.set.erasure] as indicated:
template<class Key, class Compare, class KeyContainer, class Predicate> typename flat_set<Key, Compare, KeyContainer>::size_type erase_if(flat_set<Key, Compare, KeyContainer>& c, Predicate pred);
-1- Effects: Equivalent to:auto [erase_first, erase_last] = ranges::remove_if(c, pred); auto n = erase_last - erase_first; c.erase(erase_first, erase_last); return n;-1- Preconditions:
-2- Effects: Let E beKey
meets the Cpp17MoveAssignable requirements.bool(pred(as_const(e)))
. Erases all elementse
inc
for which E holds. -3- Returns: The number of elements erased. -4- Complexity: Exactlyc.size()
applications of the predicate. -5- Remarks: Stable (16.4.6.8 [algorithm.stable]). If an invocation oferase_if
exits via an exception,c
is in a valid but unspecified state (3.65 [defns.valid]). [Note 1:c
still meets its invariants, but can be empty. — end note]
Modify 24.6.12.6 [flat.multiset.erasure] as indicated:
template<class Key, class Compare, class KeyContainer, class Predicate> typename flat_multiset<Key, Compare, KeyContainer>::size_type erase_if(flat_multiset<Key, Compare, KeyContainer>& c, Predicate pred);
-1- Effects: Equivalent to:auto [erase_first, erase_last] = ranges::remove_if(c, pred); auto n = erase_last - erase_first; c.erase(erase_first, erase_last); return n;-1- Preconditions:
-2- Effects: Let E beKey
meets the Cpp17MoveAssignable requirements.bool(pred(as_const(e)))
. Erases all elementse
inc
for which E holds. -3- Returns: The number of elements erased. -4- Complexity: Exactlyc.size()
applications of the predicate. -5- Remarks: Stable (16.4.6.8 [algorithm.stable]). If an invocation oferase_if
exits via an exception,c
is in a valid but unspecified state (3.65 [defns.valid]). [Note 1:c
still meets its invariants, but can be empty. — end note]