Re: [boost] [config] New identification system [was: Macro proposal]

From: Gennaro Prota (gennaro_prota_at_[hidden])
Date: 2006-07-13 06:03:41

On Sat, 17 Jun 2006 07:06:38 -0400, David Abrahams
<dave_at_[hidden]> wrote:

>Gennaro Prota <gennaro_prota_at_[hidden]> writes:
>
>> On Thu, 15 Jun 2006 13:19:36 -0400, David Abrahams
>> <dave_at_[hidden]> wrote:
>>
>>>   BOOST_WORKAROUND(CXX_MSVC, <=, 7,1,0)
>>>   BOOST_WORKAROUND(CXX_MSVC, tested_at, 7,1,0)
>>>
>>>is an implementable syntax.
>>
>> I'd have three questions, but maybe it's quicker to ask directly: "can
>> you post the implementation you are thinking to?"
>
>Sorry, what I was thinking of won't work because you can't paste
>anything onto "<=".

Yeah, that was one of the issues I was wondering about; you could have
been thinking of a technique which didn't involve token pasting :)
Anyway, one could of course use identifiers instead of <= and other
operators. Attached is an implementation which maps "<" to "below",
">" to "above", etc. Two of the possible invocation forms would be:

  BOOST_WORKAROUND(CXX_MSVC, last_tested, (8, 0, 0))
  BOOST_WORKAROUND(CXX_MSVC, up_to, (9, 0, 0))

Note that "CXX_MSVC" is used, though the macro actually defined is
"BOOST_CXX_MSVC" and that the version numbers are grouped into a tuple
(though this isn't necessary for the machinery to work). There's still
the comma before the tuple, as I didn't want to carry the house of
cards too far.

A further easy step would be to enable a generic placeholder, say 'x',
for minor and patch numbers, so that something like

  BOOST_WORKAROUND(CXX_CW, last_tested, (9, x, x)) // CodeW. 9.x

would be valid.

The big problem about all this is, as you know, that BOOST_PP_IS_UNARY
isn't guaranteed to work everywhere, which is why Paul didn't make it
part of the pp-lib interface. It *should* work on this scenario but
I'm not sure.

--
[ Gennaro Prota, C++ developer for hire ]
[    resume:  available on request      ]
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