fmt::to_string/compilation doesn't work with a null string_view

[DenisYaroshevskiy]

At the moment you can't fmt a default constructed string_view: https://godbolt.org/z/ddzYqYE99

[vitaut]

Specifically, this is about fmt::to_string.

[DenisYaroshevskiy]

I don't think so https://godbolt.org/z/Y6e4oPdPx

[DenisYaroshevskiy]

FYI: this is how libc++ does this: https://github.com/llvm/llvm-project/blob/ce5ef7d1d5dc632a1ff35110821a44978e004e5f/libcxx/include/__algorithm/copy.h#L60