Fix truncation warnings in string/vector iterator subtraction and ranges::is_permutation
#4237
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… iterators. Found by std/strings/basic.string/string.cons/from_range.pass.cpp. xstring(1972): warning C4244: 'return': conversion from '__int64' to 'int', possible loss of data Because we're subtracting iterators into the same string, the allocator's difference_type is always safe. Same issue with vectors.
std/containers/unord/unord.multimap/unord.multimap.cnstr/from_range.pass.cpp algorithm(940): warning C4244: 'argument': conversion from '__int64' to 'const int', possible loss of data
CaseyCarter
approved these changes
Dec 5, 2023
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I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed. |
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Test coverage will be provided by
std/strings/basic.string/string.cons/from_range.pass.cpp,std/containers/unord/unord.multimap/unord.multimap.cnstr/from_range.pass.cpp, and more in the upcoming libcxx update that I'm working on. They have allocators with custom size/difference types (e.g. 32-bit types even on 64-bit platforms) that reveal these issues.When subtracting
string/vectoriterators, we can get truncation warnings likexstring(1972): warning C4244: 'return': conversion from '__int64' to 'int', possible loss of data. Because we're subtracting iterators into the samestring/vector, casting to the allocator'sdifference_typeis always safe.In
_Is_permutation_sizedpoweringranges::is_permutation, we can getalgorithm(940): warning C4244: 'argument': conversion from '__int64' to 'const int', possible loss of data. This happens when the ranges have different difference types. We call_Is_permutation_sizedafter checking that the ranges are the same length, so we only pass the first count, and casting that to the second range's difference type is guaranteed to be value-preserving. This asymmetry looked strange enough that I thought it deserved a comment (even without introducingusing _Diff2, the line would get long enough to wrap, so we have space for a comment anyways).