[boost] Re: Constructor of iterator_adaptor takes parameter by value

From: Daniel Frey (daniel.frey_at_[hidden])
Date: 2004-01-12 10:12:39

Howard Hinnant wrote:
> On Jan 12, 2004, at 4:46 AM, Daniel Frey wrote:
> 
>> X operator+( const X& lhs, const X& rhs ) {
>>   X nrv( lhs );
>>   nrv += rhs;
>>   return nrv;
>> }
>>
>> X operator-( X lhs, const X& rhs ) {
>>   lhs += rhs;
>>   return lhs;
>> }
> 
> 
> Nice example, I see what you mean.  I hadn't thought about this case.  
> The main characteristic between this and the case I was thinking about 
> is the need to return the modified value.  IIUC, this characteristic 
> disables NRVO.

Of course. If there is no return value (RV), than neither the return 
value optimization (RVO) nor the named return value optimization (NRVO) 
can be applied. :)

> Fwiw, here is the case I was thinking about (and assumed Andrei was too):
 > [snip]

You are right: In the case you showed it's better not to take the 
parameter as a const reference but to pass it by-value. I just wanted to 
point out that there is no general rule how you should take a parameter 
which can be applied blindly without context.

Regards, Daniel

-- 
Daniel Frey
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