[Development] Setters: Passing by value or const reference?

[lars.knoll at nokia.com]

On 4/25/12 3:11 PM, "ext Olivier Goffart" <olivier at woboq.com> wrote:

>On Wednesday 25 April 2012 13:47:35 Thiago Macieira wrote:
>> However, I agree with you: it's too late to change it everywhere.
>>Unless we
>> do it properly, it also has the potential to make things worse. I'd
>>like to
>> ask you to find out where this is most important and do it now.
>
>My point was to make it the default policy for new setters rather then
>changing existing code at this point.

One problem I see here is that this does to some extent make assumptions
about the implementation of the getter. If we happen to have a need to
change the implementation, the whole point of passing by value might
suddenly become moot.

In addition it moves the code required for making the copy for the cases
where the compiler can't optimize it away to the caller, ie. from a shared
to a non shared location. This can increase the total size of the code
generated. 

So I'm absolutely not sure changing our policy is a good idea here. You
might be optimizing one case and make many others worse.

Cheers,
Lars