Reuse available string length

[mmd-osm]

No description provided.

[Woazboat]

This needs to use std::forward<T>(s) to properly pass on the forwarding reference.
(s binds to everything, but is itself a lvalue if referenced)

I don't think the template has any benefit over just inline void entry(std::string_view sv) though if a string_view is always constructed from s anyway. The function parameter will already use the appropriate constructor for string views depending on what's passed in and it should also accept a char *.

[mmd-osm]

The idea here was to avoid char* string literals ending up in entry(bool): https://godbolt.org/z/1PKz9o6dT vs. https://godbolt.org/z/ffqhjjbdh - Besides, to avoid strlen() operations in entry(const char*), which are still neded at this time, but are really pointless for string literals.

At least the generated code looks exactly as it should now. I need to check the std::forward bit still.

[Woazboat]

The idea here was to avoid char* string literals ending up in entry(bool)

Ah, yeah then that's probably required to do it this way.

The generated code will likely be the same even without std::forward since I don't believe std::string_view uses any optimization for rvalue moves.

[mmd-osm]

Yes, the optimizer even completely removes the intermediate string_view, and turns printing of string literals into something like:

   899f0:       48 8b 7d 08             mov    0x8(%rbp),%rdi
   899f4:       ba 1e 00 00 00          mov    $0x1e,%edx
   899f9:       48 8d 35 08 1b 07 00    lea    0x71b08(%rip),%rsi 
   89a00:       e8 5b 73 f9 ff          call   20d60 <yajl_gen_string@plt>

[Woazboat]

This could probably always return a std::string_view and be made constexpr.

[mmd-osm]

xml_writer::attribute expects null terminated strings at the moment, so string_view alone would trigger some intermediate object generation. We need to find a good approach that works both for json and xml.

[Woazboat]

True, using std::string_view wouldn't work for functions expecting null terminated C strings. (Well, technically you could call .data() on it, but that's best avoided since in general string_view strings don't have to be null terminated)