use `fmt::format_to` with `vector<char>` and `FMT_COMPILE`

[trim21]

I'm new to c++, apology if this is not a good issue.

I'm coming from #1771 , but I'm using a vector<char> as memory buffer.

And fmt::format_to(std::back_inserter(out), FMT_COMPILE("{}"), val) works if out is std::string of fmt::memory_buffer but not std::vector<char>, and fmt::format_to(std::back_inserter(buffer), "{}", val) works for vector<char>

Is it possible to add support for vector<char> and FMT_COMPILE?

https://godbolt.org/z/h6xoG65he

[vitaut]

Thanks for reporting. We should detect presence of append with SFINAE in

fmt/include/fmt/base.h

Lines 1974 to 1981 in 2b6a786

	// An optimized version of std::copy with the output value type (T).
	template <typename T, typename InputIt, typename OutputIt,
	FMT_ENABLE_IF(is_back_insert_iterator<OutputIt>::value)>
	FMT_CONSTEXPR20 auto copy(InputIt begin, InputIt end, OutputIt out)
	-> OutputIt {
	get_container(out).append(begin, end);
	return out;
	}

[vitaut]

Done in #4211.

[trim21]

thanks