Add UDL as replacement for FMT_COMPILE #2043
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vitaut
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Thanks for the PR! Mostly looks good, just a few nits inline.
| 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];
| ^~~~
* `FMT_USE_NONTYPE_TEMPLATE_PARAMETERS` define added * `std::size_t` changed to `size_t`
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I thought the plan was to just make compile-time checks the default in c++20? |
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@yeswalrus I think you are confusing |
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Correct, my mistake. |
include/fmt/compile.h
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| #if !defined(FMT_USE_NONTYPE_TEMPLATE_PARAMETERS) && \ | ||
| defined(__cpp_nontype_template_parameter_class) && \ | ||
| (!FMT_GCC_VERSION || FMT_GCC_VERSION >= 903) | ||
| # define FMT_USE_NONTYPE_TEMPLATE_PARAMETERS | ||
| #endif |
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Please make FMT_USE_NONTYPE_TEMPLATE_PARAMETERS defined to 1/0 for consistency with other similar macros and to make it possible to disable the feature. See e.g.
Lines 178 to 185 in 33f9a6d
| #define FMT_COMPILE(s) FMT_STRING_IMPL(s, fmt::detail::compiled_string) | ||
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| #ifdef 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.
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Merged, thanks. |
Right now {fmt} has a special macro to invoke compile-time API functions -
FMT_COMPILE. This macro can be replaced with UDL for modern compilers that support C++20. The chosen name in this PR for this feature is_cf.Note that only GCC 9.3+ support that. Clang (trunk) is also able to compile this code, but it doesn't have
__cpp_nontype_template_parameter_classdefined, I hope it'll be fixed in Clang 12 release.Proof on Compiler Explorer
constexpris used instead ofconsteval(even though it would make more sense) to lower GCC version.Also, I should note that this PR is based on my own ideas and the following comments: #1874 (comment), #613 (comment).