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

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Also added commentary for why std::strlen is directly called in certain situations.
Addresses https://github.com/fmtlib/fmt/issues/2455#issuecomment-931346096.
This commit is contained in:
Michael Winterberg 2021-09-30 11:27:31 -07:00
parent 927dbd134d
commit 3da6d3dedd
1 changed files with 9 additions and 3 deletions
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12
include/fmt/core.h
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@ -422,11 +422,17 @@ template <typename Char> class basic_string_view {
*/ */
FMT_CONSTEXPR_CHAR_TRAITS FMT_CONSTEXPR_CHAR_TRAITS
FMT_INLINE 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
if (detail::const_check(std::is_same<Char, char>::value && 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)); size_ = std::strlen(reinterpret_cast<const char*>(s));
else } else
#endif
size_ = std::char_traits<Char>::length(s); size_ = std::char_traits<Char>::length(s);
} }