Pass strings as "const std::string &" not "std::string"

[Olly Betts]

Most modern compilers seem to implement std::string using PIMPL, so the class is just a single pointer and pass-by-value may be more efficient.

MSVC is the notable exception I'm currently aware of. Macro magic is one possible solution. Or perhaps benchmarking will reveal moving helps non-MSVC without penalising MSVC much.

Either way, most of the library passes by const ref, but some of the internals pass by value, and we should standardise!

[Olly Betts]

We're certainly not going to change the internals of 1.0.x in such a sweeping way at this point, but it would be worth benchmarking this before 1.1.0 if we can.

[Olly Betts]

If this lead to changes, we'd still be API compatible so bumping to 1.1.1.

[Olly Betts]

OK, I've just microbenchmarked this for GCC 4.3.3 on x86-64 Ubuntu jaunty and const std::string & parameters are a little faster than std::string ones. Also, looking at the generated assembler shows it's more compact too!

So this bug can become "fix passing std::string by value to pass by const ref instead".

Marking for 1.1.1, as I don't think there are many of these and they should be grep-able.

[Olly Betts]

Fixed in trunk r12760.

[Olly Betts]

Fix backported to branches/1.0 r12805.