Re: [boost] Constructing string_ref from rvalue string

Subject: Re: [boost] Constructing string_ref from rvalue string
From: Gavin Lambert (gavinl_at_[hidden])
Date: 2017-03-22 22:38:09

On 23/03/2017 03:28, Olaf van der Spek via Boost wrote:
> void f2(const string&);
> string f1();
>
> f1(f2());
>
> Isn't this a very common pattern?

Yes (although you have it reversed), but that's not what we were talking 
about.  We were talking about this:

     void f1(const string_ref&);
     string f2();

     f1(f2());

Or this:

     void f1(const string_ref&);
     string_ref f2(const string_ref&);
     string f3();

     f1(f2(f3()));

They both *should* be safe because the temporary string should not be 
destroyed until after f1 is called.  But some old/embedded compilers 
would sometimes get this wrong when optimising.  You can also get into 
trouble even on modern compilers if binding is involved in certain 
patterns, since then the full-expression might end before the call 
actually happens.

I did make an error in my initial response; I've just been burned by 
buggy implementations in the past and it makes me nervous, so I jumped 
the gun.  I apologise for any confusion.