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Date: Thu, 05 Dec 2019 23:02:00 -0000
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Jonathan Wakely <jwakely.gcc@gmail.com>
Cc: Michael Matz <matz@suse.de>, Thomas Schwinge <thomas@codesourcery.com>,        "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>,        gcc-patches <gcc-patches@gcc.gnu.org>,        "fortran@gcc.gnu.org List" <fortran@gcc.gnu.org>
Subject: Re: [RFC] Characters per line: from punch card (80) to line printer (132) (was: [Patch][OpenMP/OpenACC/Fortran] Fix mapping of optional (present|absent) arguments)
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On Thu, Dec 05, 2019 at 10:37:33PM +0000, Jonathan Wakely wrote:
> On Thu, 5 Dec 2019 at 22:19, Segher Boessenkool wrote:
> > Or you could write
> >
> >     auto __c = (__builtin_memcmp(&*__first1, &*__first2, __len) <=> 0);
> >     if (__c)
> >       return __c;
> >
> > which is much easier to read, to my eyes anyway.  And it is exactly the
> > same for the compiler.
> 
> In this case yes, but not in general.
> 
> Given:
> 
> auto x = foo();
> if (bar(x))
> { }
> some_type y;
> 
> The destructor of x won't run until after y has been destroyed. That's
> not at all identical to:
> 
> if (auto x = foo(); bar(x))
> { }
> some_type y;
> 
> Please don't try to tell me how C++ works :-)

I don't, I wouldn't even *know* that.  But this is just the same as in C,
and I do know how to write good C code.

I don't think doing non-trivial things with constructors and destructors
(or anything else!) implicitly is a good idea at all, but that's an
altogether different subject.


Segher