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Made basic_string_view's const Char* constructor constexpr in C++17. #2525

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Made basic_string_view's const Char* constructor constexpr in C++17. #2525

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12 changes: 9 additions & 3 deletions include/fmt/core.h
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Original file line number Diff line number Diff line change
Expand Up @@ -422,11 +422,17 @@ template <typename Char> class basic_string_view {
*/
FMT_CONSTEXPR_CHAR_TRAITS
FMT_INLINE
basic_string_view(const Char* s) : data_(s) {
basic_string_view(const Char* s) : data_(s), size_(0) {
// This test is needed to ensure that this constructor is constexpr in C++17
// modes.
#ifdef __cpp_lib_is_constant_evaluated
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__cpp_lib_is_constant_evaluated is defined only in C++20. Therefore, code generation optimizations will not work until C++20.

if (detail::const_check(std::is_same<Char, char>::value &&
!detail::is_constant_evaluated()))
!detail::is_constant_evaluated())) {
// Call strlen directly for better code generation in non-optimized
// builds.
size_ = std::strlen(reinterpret_cast<const char*>(s));
else
} else
#endif
size_ = std::char_traits<Char>::length(s);
}

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