Re: [boost] [bind][tr1] patch for more compliant placeholders

From: Peter Dimov (pdimov_at_[hidden])
Date: 2007-05-10 07:17:02

Daniel Walker wrote:
> On 5/9/07, Peter Dimov <pdimov_at_[hidden]> wrote:
>> Daniel Walker wrote:
>>
>>>>> I've attached a patch that leaves borland and g++ <= 4.0 as they
>>>>> were. I also changed my little addition to the documentation to
>>>>> reflect this. And one more thing, I couldn't find a macro
>>>>> analogous to BOOST_MSVC for gcc's version number that I could use
>>>>> with BOOST_WORKAROUND. I added one (BOOST_GCC) in
>>>>> boost/config/compilers/gcc.hpp that does the same things as MPL's
>>>>> gcc config file. Let me know if there's some other way this should
>>>>> have been done.
>>
>> I'd like to understand the motivation behind
>> BOOST_BIND_ENABLE_INLINE_PLACEHOLDERS.
>
> I'm not sure if I entirely understand it either. ;-)
>
> I was trying to figure out why the placeholders were implemented as
> functions at all. Apparently, around version 1.5 of placeholders.h,
> inline functions were introduced for all compilers based on a
> suggestion from Yitzhak Sapir. I haven't gone back through the list
> archives to see what was under discussion at that time, but I assumed
> that an inline function implementation saved some overhead in the
> .data sections of object files. Or perhaps there was some other
> reasons that made defining the objects repeatedly in each compilation
> unit unattractive.

See

http://lists.boost.org/Archives/boost/2002/03/26490.php

and the associated thread. The specific 1.5 change is caused by Borland PCH 
problems. 1.6 has probably come right after one regression test cycle.

placeholders.hpp has evolved into its current form since many compilers 
prefer one of the implementations and have problems with the others, 
especially when using precompiled headers.