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Fix udl_compiled_string with non-byte chars (e.g. wchar) #2242

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Apr 19, 2021
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Fix udl_compiled_string with non-byte chars (e.g. wchar) #2242

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5 changes: 3 additions & 2 deletions include/fmt/compile.h
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Original file line number Diff line number Diff line change
Expand Up @@ -947,8 +947,9 @@ size_t formatted_size(const CompiledFormat& cf, const Args&... args) {
#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>
constexpr detail::udl_compiled_string<
remove_cvref_t<decltype(Str.data[0])>,
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Can we move remove_cvref_t<decltype(Str.data[0])> to a default template parameter to avoid repetition? i.e.

template <detail::fixed_string Str, Char = remove_cvref_t<decltype(Str.data[0])>>

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Looks like it's not possible because compilers expect to see certain template arguments - https://godbolt.org/z/6odY6E78h

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Can we at least do typename Str::char_type?

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How about value_type as in basic_string<>::value_type ?

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Sure, value_type is a more appropriate.

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@alexezeder alexezeder Apr 19, 2021 •
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Don't forget that Str is not a type, it's an object since it's passed as a non-type template parameter, so we have these options here:

<remove_cvref_t<decltype(Str.data[0])>, sizeof(Str.data) / sizeof(decltype(Str.data[0])), Str>
vs.
<typename decltype(Str)::value_type, sizeof(Str.data) / sizeof(typename  decltype(Str)::value_type), Str>

and they both are not great.

But the size of fixed_string can be exposed by a static member or function, like so:

<typename decltype(Str)::value_type, decltype(Str)::size, Str>

Just let me know if this approach is preferable.

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I think it's fine as is then. Thanks for the fix.

sizeof(Str.data) / sizeof(decltype(Str.data[0])), Str>
operator""_cf() {
return {};
}
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1 change: 1 addition & 0 deletions test/compile-test.cc
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Expand Up @@ -316,6 +316,7 @@ TEST(CompileTest, CompileFormatStringLiteral) {
using namespace fmt::literals;
EXPECT_EQ("", fmt::format(""_cf));
EXPECT_EQ("42", fmt::format("{}"_cf, 42));
EXPECT_EQ(L"42", fmt::format(L"{}"_cf, 42));
}
#endif

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