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Add UDL as replacement for FMT_COMPILE #2043

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merged 6 commits into from
Dec 7, 2020
Merged

Add UDL as replacement for FMT_COMPILE #2043

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506230b
add _cf literal as replacement for FMT_COMPILE
alexezeder Dec 1, 2020
8c8b1cc
apply requested changes
alexezeder Dec 2, 2020
855e488
add empty format string into CompileTest::CompileFormatStringLiteral
alexezeder Dec 2, 2020
6ea2ca8
fix for empty format string
alexezeder Dec 2, 2020
b81bf00
update FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
alexezeder Dec 7, 2020
e7d035d
remove deduction guide for `fixed_string`
alexezeder Dec 7, 2020
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38 changes: 38 additions & 0 deletions include/fmt/compile.h
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,15 @@

#include "format.h"

#ifndef FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
# if defined(__cpp_nontype_template_parameter_class) && \
(!FMT_GCC_VERSION || FMT_GCC_VERSION >= 903)
# define FMT_USE_NONTYPE_TEMPLATE_PARAMETERS 1
# else
# define FMT_USE_NONTYPE_TEMPLATE_PARAMETERS 0
# endif
#endif

FMT_BEGIN_NAMESPACE
namespace detail {

Expand All @@ -37,6 +46,24 @@ struct is_compiled_string : std::is_base_of<compiled_string, S> {};
*/
#define FMT_COMPILE(s) FMT_STRING_IMPL(s, fmt::detail::compiled_string)

#if FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
template <typename Char, size_t N> struct fixed_string {
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Is fixed_string actually needed? Can we directly use an array instead?

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Looks like yes, it's actually needed. The raw C-style array should be wrapped in some type, and this wrapper-type should also have a constructor with const Char (&str)[N] as an argument. Of course, I can be wrong here, but all my attempts ended up with nothing working.

But I realized that the deduction guide for fixed_string can be removed now because it holds a null-terminated string.

constexpr fixed_string(const Char (&str)[N]) {
copy_str<Char, const Char*, Char*>(static_cast<const Char*>(str), str + N,
data);
}
Char data[N]{};
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{} seems unnecessary, please remove.

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It's either {} here or : data{} initialization in constructor for GCC 9.3, otherwise:

<source>:8:13: error: member 'fmt::v7::detail::fixed_string<char, 2>::data' must be initialized by mem-initializer in 'constexpr' constructor
<source>:12:8: note: declared here
   12 |   Char data[N];
      |        ^~~~

};

template <typename Char, size_t N, fixed_string<Char, N> Str>
struct udl_compiled_string : compiled_string {
using char_type = Char;
constexpr operator basic_string_view<char_type>() const {
return {Str.data, N - 1};
}
};
#endif

template <typename T, typename... Tail>
const T& first(const T& value, const Tail&...) {
return value;
Expand Down Expand Up @@ -698,6 +725,17 @@ size_t formatted_size(const CompiledFormat& cf, const Args&... args) {
return format_to(detail::counting_iterator(), cf, args...).count();
}

#if FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
inline namespace literals {
template <detail::fixed_string Str>
constexpr detail::udl_compiled_string<remove_cvref_t<decltype(Str.data[0])>,
sizeof(Str.data), Str>
operator""_cf() {
return {};
}
} // namespace literals
#endif

FMT_END_NAMESPACE

#endif // FMT_COMPILE_H_
8 changes: 8 additions & 0 deletions test/compile-test.cc
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Expand Up @@ -179,6 +179,14 @@ TEST(CompileTest, Empty) {
}
#endif

#if FMT_USE_NONTYPE_TEMPLATE_PARAMETERS
TEST(CompileTest, CompileFormatStringLiteral) {
using namespace fmt::literals;
EXPECT_EQ("", fmt::format(""_cf));
EXPECT_EQ("42", fmt::format("{}"_cf, 42));
}
#endif

#if __cplusplus >= 202002L
template <size_t max_string_length> struct test_string {
template <typename T> constexpr bool operator==(const T& rhs) const noexcept {
Expand Down