Re: [boost] Bind comparisons

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-08-13 05:27:13

David Abrahams wrote:
> "Peter Dimov" <pdimov_at_[hidden]> writes:
>
>> David Abrahams wrote:
>>> Is it really true that I can write
>>>
>>>   bind(f, _1) > _2
>>>
>>> but can't write
>>>
>>>    _1 > _2
>>>
>>> ??
>>>
>>> I can't imagine a good reason for that restriction, but I don't see
>>> any indication that the latter is supported in the docs.
>>
>> A limitation of the current implementation. On some compilers, the
>> placeholders are function pointers and _1 > _2 can't be
>> overloaded. There's no other technical reason that prevents _1 > _2
>> (or _1 > 0) from working; it'd fall out of the specification.
>
> Thanks for the info.
>
> What abut the trick of making the placeholders references in an
> unnamed namespace to objects in a named one?

The problem is that on some compilers we can't define objects in precompiled 
headers. This is not an issue for TR1 because the placeholders are only 
declared 'extern' in the header, only for the Boost implementation ("least 
common denominator" for historical reasons :-)