Revise arguments which were being passed by value instead of as a reference

[SunBlack]

Fixed all passedByValue hints by CppCheck 1.85

[jasjuang]

I believe pass vectors by reference makes sense but strings should be passed by value because of SSO.

Please see https://stackoverflow.com/a/10232761/3667089

[SergioRAgostinho]

@jasjuang What the article you pointed is saying is that if you need to create a copy of the string, inside the function, for any given reason, then you should definitely pass by value.

[SergioRAgostinho]

Nb: I'm not marking this as an ABI change because it is just targeted at apps and tools. Nothing on the main libs public interface.

[jasjuang]

@SergioRAgostinho Yes, but that's an extra precaution that needs to be taken into account. Passing in small strings as value is not more expensive because of SSO. My point is there is one more boundary condition for const & to check for verses pass by value yet there isn't any gain over it, so why bother to make the change?

[SergioRAgostinho]

If a string meets the SSO length criteria, then it is allocated on the stack. Great for constructors and move mechanics. It's good that it exists when we qualify for it, but I can only rely on the assumptions that my string is going to be small in a couple of controlled cases. This lenght criteria is implementation defined but for libc++ appears to be 3 words, and according to the answer yields 10 chars on a 32 bit machine, 22 chars on a 64bit. So you're copying 24bytes vs a pointer (8 bytes) in the best case.

The claimed benefit is that one doesn't need to care about it anymore because in most cases SSO will kick in and it's a minor stack copy, if the string is short. Also you don't have to write the extra const and &.

In the opposite case, you obviously write const & but what exactly is the downside of this approach?

[jasjuang]

If we can't assume the string to be small I agree const & is a better idea. Thanks for showing me the link. That was an interesting read!