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match_results does not specify the semantics of operator==Section: 28.6.9.9 [re.results.nonmember] Status: Resolved Submitter: Daniel Krügler Opened: 2010-10-24 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
The Returns element of operator== says:
trueonly if the two objects refer to the same match
It is not really clear what this means: The current specification would allow for an
implementation to return true, only if the address values of m1 and
m2 are the same. While this approach is unproblematic in terms of used operations
this is also a bit unsatisfactory. With identity equality alone there seems to be no convincing
reason to provide this operator at all. It could for example also refer to an comparison based
on iterator values. In this case a user should better know that this will be done, because
there is no guarantee at all that inter-container comparison of iterators
is a feasible operation. This was a clear outcome of the resolution provided in
N3066
for LWG issue 446(i).
It could also mean that a character-based comparison of the individual sub_match
elements should be done - this would be equivalent to applying operator== to
the subexpressions, prefix and suffix.
Proposed resolution:
Addressed by paper n3158.