RE: [Boost-Users] Re: "Correct" way to return empty shared_ptr?

From: Ben Hutchings (ben.hutchings_at_[hidden])
Date: 2003-04-24 12:36:27

dick.bridges_at_[hidden] wrote:
> This is one of the places where I get *REALLY* confused - the 'real'
code
> has multiple returns.  Apologies:  I should have included this psuedo
code
> in the original example.  It looks like this.
> 
> <snippet>
> // v is populated somewhere else
> typedef vector<shared_ptr<int> > V;
> V v;
> 
> shared_ptr<int> maybe_get_a_pointer()
> {
>     shared_ptr<int>::iterator itr;
>     itr = find_if(v.begin(), v.end(), some_op);
> 
>     if(itr != v.end)
>         return(*itr);
> 
>     shared_ptr<int> p;
>     return(p);
> }
> </snippet>
> 
> Are compilers supposed to be able to match *itr to p in order to apply
the
> NRVO?

I don't know what you mean by "match *itr to p".

The NRVO should be possible for the second return statement, because if
p is constructed then it's always returned.  However, optimisations are
by definition optional so the implementation isn't "supposed to" perform
them.