Optimize %T in tm formatting

[phprus]

Optimization %T in tm formatting like this: 67cb2da

And fix wchar_t tm formatting error:

/.../fmt/include/fmt/chrono.h:567:15: error: no match for ‘operator==’ (operand types are ‘fmt::v8::basic_string_view<wchar_t>’ and ‘fmt::v8::string_view {aka fmt::v8::basic_string_view<char>}’)
     if (specs == string_view("%F", 2))

Maybe I should add the use of write_digit2_separated for formats:

• %Y-%m-%d
• %H:%M:%S
• %Y-%m-%d %H:%M:%S
• %Y-%m-%dT%H:%M:%S

?

[miscco]

There is no basic_string_view<> before C++17.

Could it be that the internal replacement should be updated?

[phprus]

Problem in std::char_traits<>::compare:

fmt/include/fmt/core.h

Lines 472 to 478 in 3d0c7ae

	FMT_CONSTEXPR_CHAR_TRAITS auto compare(basic_string_view other) const -> int {
	size_t str_size = size_ < other.size_ ? size_ : other.size_;
	int result = std::char_traits<Char>::compare(data_, other.data_, str_size);
	if (result == 0)
	result = size_ == other.size_ ? 0 : (size_ < other.size_ ? -1 : 1);
	return result;
	}

constexpr std::char_traits<>::compare starts from C++17 only

[vitaut]

Thanks for the PR!

[vitaut]

What is this for?

[phprus]

Oh! Removed.

[vitaut]

Maybe I should add the use of write_digit2_separated for formats

I'm not sure if we should add more special cases but it would be nice to get rid of strftime completely in formatter::format by parsing the format string and using the optimization when possible. It would be not as fast as special casing but would be more generally applicable.