Re: [boost] rvalue ref best practices?

Subject: Re: [boost] rvalue ref best practices?
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-06-11 07:22:01

On 11/06/2012 13:14, Giovanni Piero Deretta wrote:

> Apart from the fact that "an arbitrary place" in your sentence would
> seem to cover anything

You don't get to choose where. The compiler does.

> to what subobject are you referring to?

Any subobject. Or any specific storage really.

> The
> only thing I can think of is assignment operators of derived classes
> that need to forward to base classes. In that case I agree that pass
> by value does not work very well (I usually still use pass by value,
> but implement operator= in term of swap, which forwards to the base
> class swap).

According to this rule, I should pass by value whenever I want to copy 
the variable anyway.

template<class T>
struct foo
{
   T t;
   foo(T t_) : t(t_) {}
};

Clearly we can see this code causes one copy with rvalues, two with 
lvalues, instead of always one if we used const-reference.

The only instance where this might be useful is operator=, and then 
again, it's probably still a bad idea.

I had already pointed out to Dave that the way the rule as worded was 
incorrect.