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Enable FMT_STRING() use with types other than string literals

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Scott Ramsby 2020-03-11 17:43:14 -07:00 committed by Victor Zverovich
parent 69779b4ed6
commit 664dd88e31
3 changed files with 43 additions and 14 deletions
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3
include/fmt/core.h
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@ -371,6 +371,9 @@ template <typename Char> class basic_string_view {
the size with ``std::char_traits<Char>::length``.
\endrst
*/
#if __cplusplus >= 201703L // C++17's char_traits::length() is constexpr.
FMT_CONSTEXPR
#endif
basic_string_view(const Char* s)
: data_(s), size_(std::char_traits<Char>::length(s)) {}

40
include/fmt/format.h
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@ -2238,6 +2238,7 @@ enum class arg_id_kind { none, index, name };
// An argument reference.
template <typename Char> struct arg_ref {
FMT_CONSTEXPR arg_ref() : kind(arg_id_kind::none), val() {}
FMT_CONSTEXPR explicit arg_ref(int index)
: kind(arg_id_kind::index), val(index) {}
FMT_CONSTEXPR explicit arg_ref(basic_string_view<Char> name)
@ -3525,9 +3526,21 @@ template <typename Char> struct udl_arg {
}
};
// Converts string literals to basic_string_view.
template <typename Char, size_t N>
FMT_CONSTEXPR basic_string_view<Char> literal_to_view(const Char (&s)[N]) {
return {s, N - 1};
FMT_CONSTEXPR basic_string_view<Char> compile_string_to_view(
const Char (&s)[N]) {
// Remove trailing null character if needed. Won't be present if this is used
// with raw character array (i.e. not defined as a string).
return {s,
N - ((std::char_traits<Char>::to_int_type(s[N - 1]) == 0) ? 1 : 0)};
}
// Converts string_view to basic_string_view.
template <typename Char>
FMT_CONSTEXPR basic_string_view<Char> compile_string_to_view(
const std_string_view<Char>& s) {
return {s.data(), s.size()};
}
} // namespace internal
@ -3585,18 +3598,17 @@ FMT_CONSTEXPR internal::udl_arg<wchar_t> operator"" _a(const wchar_t* s,
#endif // FMT_USE_USER_DEFINED_LITERALS
FMT_END_NAMESPACE
#define FMT_STRING_IMPL(s, ...) \
[] { \
/* Use a macro-like name to avoid shadowing warnings. */ \
struct FMT_COMPILE_STRING : fmt::compile_string { \
using char_type = fmt::remove_cvref_t<decltype(*s)>; \
FMT_MAYBE_UNUSED __VA_ARGS__ FMT_CONSTEXPR \
operator fmt::basic_string_view<char_type>() const { \
/* FMT_STRING only accepts string literals. */ \
return fmt::internal::literal_to_view(s); \
} \
}; \
return FMT_COMPILE_STRING(); \
#define FMT_STRING_IMPL(s, ...) \
[] { \
/* Use a macro-like name to avoid shadowing warnings. */ \
struct FMT_COMPILE_STRING : fmt::compile_string { \
using char_type = fmt::remove_cvref_t<decltype(s[0])>; \
FMT_MAYBE_UNUSED __VA_ARGS__ FMT_CONSTEXPR \
operator fmt::basic_string_view<char_type>() const { \
return fmt::internal::compile_string_to_view<char_type>(s); \
} \
}; \
return FMT_COMPILE_STRING(); \
}()
/**

14
test/format-test.cc
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@ -46,6 +46,7 @@ using fmt::format_error;
using fmt::memory_buffer;
using fmt::string_view;
using fmt::wmemory_buffer;
using fmt::wstring_view;
using fmt::internal::basic_writer;
using fmt::internal::max_value;
@ -1854,10 +1855,23 @@ TEST(FormatTest, UnpackedArgs) {
struct string_like {};
fmt::string_view to_string_view(string_like) { return "foo"; }
constexpr char with_null[3] = {'{', '}', '\0'};
constexpr char no_null[2] = {'{', '}'};
TEST(FormatTest, CompileTimeString) {
EXPECT_EQ("42", fmt::format(FMT_STRING("{}"), 42));
EXPECT_EQ(L"42", fmt::format(FMT_STRING(L"{}"), 42));
EXPECT_EQ("foo", fmt::format(FMT_STRING("{}"), string_like()));
(void)with_null;
(void)no_null;
#if __cplusplus >= 201703L
EXPECT_EQ("42", fmt::format(FMT_STRING(with_null), 42));
EXPECT_EQ("42", fmt::format(FMT_STRING(no_null), 42));
#endif
#if defined(FMT_USE_STRING_VIEW) && __cplusplus >= 201703L
EXPECT_EQ("42", fmt::format(FMT_STRING(std::string_view("{}")), 42));
EXPECT_EQ(L"42", fmt::format(FMT_STRING(std::wstring_view(L"{}")), 42));
#endif
}
TEST(FormatTest, CustomFormatCompileTimeString) {