Re: [boost] more flexible lexical_cast

From: Rob Stewart (stewart_at_[hidden])
Date: 2002-08-22 14:00:32

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From: =?Windows-1252?Q?Terje_Sletteb=F8?= <tslettebo_at_[hidden]>
> 
> >From: "Rob Stewart" <stewart_at_[hidden]>
> 
> > From: "Victor A. Wagner, Jr." <vawjr_at_[hidden]>
> > >
> > > At Thursday 2002/08/22 03:44, you wrote:
> >
> > These attributions are not very helpful.  Who's "you?"
> 
> Me. :)

Unfortunately, his attribution line doesn't make that clear.

> > The swap is still valuable because it swaps the contents between widget
> and the
> > temporary returned by ost.str().  The alternative, assigning the temporary
> to
> > widget, means that a copy of the temporary's contents is written to widget
> and
> > then the temporary is destroyed.
> 
> But in what way would this be useful for lexical_cast?

That may well be a separate question from the one I was answering!

> if you have std::string as target, you have something like:
> 
> std::stringstream interpreter;
> 
> ...
> 
> return std::string(interpreter.c_str());
> 
> How will a swap help you here?

My guess is that you meant:

    return std::string(interpreter.str());

In that case, swap() is not useful, since this line makes explicit the copy
construction that must -- in theory -- occur anyway.  (Actually, I'm left to
wonder whether this tells the compiler to invoke the copy constructor, thus
preventing the RVO.)  There is no place for a swap to occur as there is no named
return value to swap with and str() already creates a copy of the
stringstream's internal buffer.

-- 
Rob Stewart                           stewart_at_[hidden]
Software Engineer                     http://www.sig.com
Susquehanna International Group, LLP  using std::disclaimer;