Fix set::min()/max() comparator bug and non-const operator[] (#28)#32
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set::min()/max() used std::min_element/std::max_element, which rank by operator< instead of the set's TCompare. For sets with a custom comparator this returned the wrong element, required operator< even when a comparator was supplied, and was O(n). They now return *begin() / *std::prev(end()), which respects the comparator and is O(1). The non-const set::operator[] did `auto it = std::advance(begin(), index)`, but std::advance returns void, so the overload failed to compile whenever instantiated (subscripting a non-const set). It now advances an iterator in place, matching the const overload, and works on both C++11 and C++17. Added tests: min/max with a comparator that differs from operator< (descending int comparator), and non-const subscripting.
GitHub's windows-latest image no longer provides the "Visual Studio 17 2022" generator, so CMake configure failed with "could not find any instance of Visual Studio" before compiling. Pin the Windows matrix entries to windows-2022.
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Summary
Fixes the two correctness defects in
include/set.htracked in #28.1.
set::min()/max()ignored the set's comparatorThey used
std::min_element/std::max_element, which rank byoperator<rather than the set'sTCompare. For a set with a custom comparator this returned the wrong element, requiredoperator<even when a comparator was supplied, and ran in O(n). They now return*begin()/*std::prev(end())(guarded by an emptiness check), which respects the comparator and is O(1).2. Non-const
set::operator[]did not compileIt did
auto it = std::advance(begin(), index);, butstd::advancereturnsvoid, so the overload failed to compile whenever instantiated (i.e. subscripting a non-const set). It now advances an iterator in place, matching the const overload, and works on both C++11 and C++17.Tests
MinRespectsCustomComparator/MaxRespectsCustomComparatorusing a descending int comparator (which differs fromoperator<), so they isolate the actual defect.NonConstSubscripting, which subscripts a non-const set (previously a compile error).Verification
Note
The pre-existing
MinCustomType/MaxCustomTypetests keep their#if defined(__clang__)/#if __linux__branches:person_comparatoris defined asa < b(hash-based, i.e. identical tooperator<), so their cross-platform divergence comes fromstd::hashdiffering between libc++ and libstdc++ — unrelated to this bug — and this fix leaves their results unchanged.Closes #28.
https://claude.ai/code/session_011y3XcVg3UCcgi5JMEo2tso
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