Re: [boost] Proposal for #pragma once support

Subject: Re: [boost] Proposal for #pragma once support
From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2009-06-09 16:14:07

On Tue, Jun 9, 2009 at 9:57 PM, John
Phillips<phillips_at_[hidden]> wrote:
> Zachary Turner wrote:
>
>> I agree that it would need to be automated.  But the script itself should
>> be
>> very trivial, I'd be willing to try it myself.  And perhaps the best
>> approach is what I mentioned in a previous post, to force the programmer
>> to
>> explicitly define BOOST_USE_PRAGMA_ONCE before including a boost header
>> file.  This would solve the problem of having to modify every header when
>> new compilers were released.  And since by default it would be undefined,
>> an
>> out-of-the-box boost installation would work exactly as it does now.  I'll
>> work on this a bit later today perhaps, and try to post some benchmarks
>> for
>> for compiling boost itself, and for compiling a commercial product which
>> uses boost.
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>
>  I have a dim memory that there used to be some libraries that did not have
> include guards, and would fail without them because of recursive use of
> headers. Is that still true, or am I hallucinating about it?
>

Pretty much anything that uses Boost.Preprocessor with file iteration.
 And of course, Boost.Preprocessor itself.
Also, IIRC, some libraries do not use boost.preprocessor directly, but
implement some crude form of file iteration directly (which will also
break).

HTH,

-- 
gpd