quotes for string support.

[Remotion]

std::string and types like it are now printed in double quotes "str".
chars are now printed in single quotes 'A'.

#include <tuple>
#include <vector>
#include <string_view>

#define FMT_HEADER_ONLY
#include <fmt/ranges.h>

int main() {
    std::tuple tup = {1, '1', "10", std::string("20"), std::string_view{"30"}};
    fmt::print("{}\n", tup); // (1, '1', "10", "20", "30")

    std::vector vec = {'1', '2'};
    fmt::print("{}\n", vec); // {'1', '2'}

    std::vector vec2 = {"2", "3"};
    fmt::print("{}\n", vec2); // {"2", "3"}
}

[vitaut]

nit: could you wrap long (>80 char length) lines per the style guide (https://google.github.io/styleguide/cppguide.html#Line_Length) here and below?

[Sarcasm]

It would be nice if the quoting worked the same as std::quoted.
That is, embedded quotes are escaped too.

Also, I'm would really love it if there was something similar to python format's value conversion flag:

• https://pyformat.info/#conversion_flags

Notably, an equivalent to the !r flag.

That is:

std::string s = "abc \"def\" hij";
fmt::print("s is: {!r}\n", s);

Would output:

s is: "abc \"def\" hij"

The reason I'm asking for this, is when formatting error messages.
If I get an invalid string value, which might be a path, an executable name, or anything else.
I'd like to make sure my error messages fits on one line and is somewhat unambiguous:

No quote at all:

error: Value abc def is not valid.
error: Value abc "def is not valid.
error: Value abc
def is not valid.
error: Invalid value: abc def

Vs "dumb quotes" (fmt::format(""{}"", value)):

error: Value "abc def" is not valid.
error: Value "abc "def" is not valid.
error: Value "abc
def" is not valid.
error: Invalid value: "abc def  "

Vs string representation:

error: Value "abc def" is not valid.
error: Value "abc \"def" is not valid.
error: Value "abc\ndef" is not valid.
error: Invalid value: "abc def  "

Note: std::quoted does not handle newline specifically.

Sorry if this comment is out of scope for this PR.

[vitaut]

It would be nice if the quoting worked the same as std::quoted.

That makes sense, but I suggest doing it in a separate PR.

[SuperWig]

Would it be a good idea to have an is_char type trait so people have the option to add support for their own chars?

[Remotion]

Adding fmt::is_char and use it instate of function specialization for char ?

How about char, wchar_t, char16_t, char32_t ?

[SuperWig]

Yeah was thinking something like

template <typename T>
struct is_char : std::integral_constant<bool,
	std::is_same<char, T>::value ||
	std::is_same<char16_t, T>::value ||
	std::is_same<char32_t, T>::value> {};
---------------
template<typename Arg>
FMT_CONSTEXPR const char* format_str_quoted(bool add_space, const Arg&, 
    typename std::enable_if<!is_like_std_string<typename  std::decay<Arg>::type>::value &&
	!is_char<typename std::decay<Arg>::type>::value>::type* = nullptr) {
  return add_space ? " {}" : "{}";
}
------------------------
template <typename Arg>
FMT_CONSTEXPR const char* format_str_quoted(bool add_space, const Arg&,
	typename std::enable_if<is_char<typename std::decay<Arg>::type>::value>::type* = nullptr) {
    return add_space ? " '{}'" : "'{}'";
}

Though wouldn't you need to separate wchar_t since it uses a different format? And apparently char16_t and char32_t aren't supported by fmt. I get this error

fmt\core.h(541) error C2079: 'f' uses undefined struct 'fmt::v5::formatter<T,char,void>'

[vitaut]

@Remotion, merged, thanks! Could you by any chance submit a section about the new ranges functionality including quotation to the docs?