Re: [boost] Constructing string_ref from rvalue string

Subject: Re: [boost] Constructing string_ref from rvalue string
From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2017-03-22 22:50:53

On 03/23/17 01:38, Gavin Lambert via Boost wrote:
> 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.

IMHO, compiler bugs should not be the reason for interface design 
choices. And BTW, I know Sun Pro compiler (Oracle Studio nowdays) had a 
mode with the opposite behavior - it would not destroy temporaries until 
the end of the scope.

>  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.

Whatever we decide to do about this issue, I think we should make the 
choice before 1.64 is released. I think, this is a new change for 1.64, 
and it's not too late to roll it back if we choose so (IMHO, we should).