On a Windows build using clang-cl, the build of //riegeli/records/record_reader fails with:
external/riegeli+/riegeli/records/record_reader.cc(651,9): error: call to 'BinarySearch' is ambiguous
651 | BinarySearch(
| ^~~~~~~~~~~~
external/riegeli+\riegeli/base/binary_search.h(375,26): note: candidate function [with Pos = unsigned long long, Test = (lambda at external/riegeli+/riegeli/records/record_reader.cc:653:13), $2 = 0]
375 | inline SearchResult<Pos> BinarySearch(Pos low, Pos high, Test&& test) {
| ^
external/riegeli+\riegeli/base/binary_search.h(454,41): note: candidate function [with Pos = unsigned long long, Test = (lambda at external/riegeli+/riegeli/records/record_reader.cc:653:13), $2 = 0]
454 | inline std::optional<SearchResult<Pos>> BinarySearch(Pos low, Pos high,
| ^
The call in question is here:
It has the signature:
BinarySearch(uint64_t, uint64_t, std::optional<PartialOrdering>(uint64_t record_index));
But the compiler thinks it matches the plain overload:
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template < |
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typename Pos, typename Test, |
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std::enable_if_t<binary_search_internal::TestReturnsOrderingOrSearchGuide< |
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Test, Pos>::value, |
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int>> |
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inline SearchResult<Pos> BinarySearch(Pos low, Pos high, Test&& test) { |
As well as the std::optional one:
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template <typename Pos, typename Test, |
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std::enable_if_t< |
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binary_search_internal::TestReturnsOptionalOrderingOrSearchGuide< |
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Test, Pos>::value, |
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int>> |
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inline std::optional<SearchResult<Pos>> BinarySearch(Pos low, Pos high, |
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Test&& test) { |
It should match the latter, the test returns std::optional<PartialOrdering>, and that should match if PartialOrdering satisfies IsOrdering, which is defined as:
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template <typename T, typename Enable = void> |
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struct IsOrdering : std::false_type {}; |
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|
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template <typename T> |
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struct IsOrdering<T, std::void_t<decltype(std::declval<T>() < 0), |
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decltype(std::declval<T>() > 0), |
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decltype(std::declval<T>() == 0)>> |
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: std::true_type {}; |
So it should match if all of <, >, and == are defined when the other arg is 0. But if that applies to T, shouldn't it also apply to std::optional<T>? It does seem like the way those comparison operators are derived differs in C++20, the other comparison operators for std::optional are derived from <=> starting in C++20. But I'm still very confused why the error is only coming up with clang-cl on Windows and not Clang on other platforms.
On a Windows build using clang-cl, the build of
//riegeli/records/record_readerfails with:The call in question is here:
riegeli/riegeli/records/record_reader.cc
Line 651 in a5d3729
It has the signature:
But the compiler thinks it matches the plain overload:
riegeli/riegeli/base/binary_search.h
Lines 370 to 375 in a5d3729
As well as the
std::optionalone:riegeli/riegeli/base/binary_search.h
Lines 449 to 455 in a5d3729
It should match the latter, the test returns
std::optional<PartialOrdering>, and that should match ifPartialOrderingsatisfiesIsOrdering, which is defined as:riegeli/riegeli/base/compare.h
Lines 67 to 74 in a5d3729
So it should match if all of
<,>, and==are defined when the other arg is0. But if that applies toT, shouldn't it also apply tostd::optional<T>? It does seem like the way those comparison operators are derived differs in C++20, the other comparison operators forstd::optionalare derived from<=>starting in C++20. But I'm still very confused why the error is only coming up with clang-cl on Windows and not Clang on other platforms.