Re: Making use of move semantics?

[Murray Cumming <murrayc murrayc com>]

On Sun, 2017-05-21 at 10:36 +0100, Daniel Boles wrote:
> I still occasionally find myself reflexively std::move()ing strings
> into glibmm/gtkmm functions that I unconsciously see as taking
> ownership of their arguments - only to realise it makes no difference
> because all of them take strings as const&.
>
> This made me wonder whether there are any cases where, if the user
> instructs so by using std::move(), glibmm/gtkmm functions could steal
> the string [ or at least it's c_str() ] and thus avoid having to copy
> it. All those copies quickly add up to a lot.
>
> But my suspicion, without yet having dived into the code, is that
> most or all functions like this just take the c_str() and pass that
> to the underlying C methods, which would just see it as a char const*
> and copy it anyway - meaning we wouldn't be able to gain much or
> anything on the mm side.
>
> Are my initial suspicions accurate, or are there any cases in which
> we can use move semantics to avoid copies, either on the mm or C
> sides?

We've already used move/r-value-references in several places, but not
for string arguments.

I guess we might start taking std::string_view with C++17 instead of
std::string and this might largely take care of this.

> Assuming nothing can be done here, if anyone can think of any other
> cases where we could make use of move semantics, that'd be a nice
> consolation prize. :D


-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com