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

From: Duane Murphy (duanemurphy_at_[hidden])
Date: 2003-04-24 11:40:36

--- At Thu, 24 Apr 2003 16:56:40 +0100, Ben Hutchings wrote:

>dick.bridges_at_[hidden] wrote:
>> I don't understand C++ well enough to grok a compiler's interpretation
>of
>> the code, but I seems like I'm creating an extra copy for the return.
><snip>
>
>Logically the local variable is copied to the the caller, but since the
>type
>of the returned expression matches the return type the compiler is
>allowed
>to optimise away that copy, even though the return type has a
>user-defined
>copy constructor.  In this case you always return a certain named
>variable,
>so the compiler can arrange to construct it in the memory location where
>the
>caller expects the returned value.  This is called the
>named-return-value
>optimisation, or NRVO.

I dont want to start any kind of war, and this is a bit off topic, but I
was investigating NVRO and found a few discussions with Scott Meyers that
indicated that naming is not relevant to the optimization. That this:

shared_ptr<int> maybe_get_a_pointer()
{
      return shared_ptr<int>();
}

is perfectly reasonable and can also be optimized.

Is there more recent and complete discussion concerning this
optimization? Is naming actually required?

 ...Duane