string + string_view operators

[OlafvdSpek]

It'd be nice if the following (and more) operators were supported in Boost for std::string, boost::string_ref and boost::string_view. Since the standard doesn't provide them (yet) for std::string_view having them for that type would be great as well.

s += sv;
s + sv;
sv + s;
sv + sv; ?

[mclow]

Let's talk about what these might do:
s += sv --> append the contents of sv to the string s.
s + sv --> create a new string with the contents of sv appended to the contents of s.
sv + s --> create a new string with the contents of s appended to the contents of sv.
sv1 + sv2 --> create a new string with the contents of sv1 appended to the contents of sv2.

I think that the last three are unwelcome. Silently creating a string when you're manipulating string_views is not (IMHO) a good idea.

[OlafvdSpek]

Why?
AFAIK string_view is supposed to be a drop-in replacement for string in most cases, hence all member functions..
What would be the problem with s + sv?
string + const char* works fine.

[OlafvdSpek]

s << s and s << sv would be nice too. They'd not create new strings and look similar to stream output operations.

[mclow]

I'm not sure what you mean by s << s or s << sv. What operation would happen here?
I think you're right about s + sv, though.

[OlafvdSpek]

s += s and s += sv, respectively. Like stringstream but using string instead.

It'd allow for a more efficient way to do:

string s;
s += A + B + to_string(42) + C; // mind the temporaries
s << A << B << to_string(42) << C;

s << A << B << 42 << C; // maybe even support integers and floats