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Enable named arguments check in compile-time checks #2649

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Dec 17, 2021
Merged

Enable named arguments check in compile-time checks #2649

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8 changes: 7 additions & 1 deletion include/fmt/core.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1109,6 +1109,11 @@ template <typename... Args> constexpr auto count_named_args() -> size_t {
return count<is_named_arg<Args>::value...>();
}

template <typename... Args>
constexpr auto count_statically_named_args() -> size_t {
return count<is_statically_named_arg<Args>::value...>();
}

enum class type {
none_type,
// Integer types should go first,
Expand Down Expand Up @@ -3043,7 +3048,8 @@ template <typename Char, typename... Args> class basic_format_string {
std::is_reference<Args>::value)...>() == 0,
"passing views as lvalues is disallowed");
#ifdef FMT_HAS_CONSTEVAL
if constexpr (detail::count_named_args<Args...>() == 0) {
if constexpr (detail::count_named_args<Args...>() ==
detail::count_statically_named_args<Args...>()) {
Comment on lines +3051 to +3052
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Doesn't this effectively make fmt::arg unusable?

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As far as I understand, fmt::arg is handled the same way as before. Consider the following table with results of boolean expressions inside this if:

master PR
w/o named arguments true true
fmt::arg false false
_a false true
fmt::arg + _a false false

This way, nothing should change for fmt::arg. In contrast with format string with a mix of named and non-named arguments.

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Makes sense.

using checker = detail::format_string_checker<Char, detail::error_handler,
remove_cvref_t<Args>...>;
detail::parse_format_string<true>(str_, checker(s, {}));
Expand Down