[boost] Re: Constrained genericity at last? (any interest in anoperator traits/concept traits library?)

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2004-09-28 18:29:59

Terje Slettebø wrote:
>>From: "Terje Slettebø"
>  
> If we get a version of has_plus_op using this technique, we could compare it
> to the current version, in terms of dependencies, compilation speed
> (instantiating it with a lot of types), etc.
>

Hi again,

got a modified version of your operator+ detection ready, which passes 
your test unit.

    http://tinyurl.com/6gtn2

Nearly all dependecies are gone - I kept 'mpl::and_' (just because I was 
too lazy to change things which are likely to change again ;+) - 
actually we can get rid of this, too.
( For that matter it's probably a good idea to use these 
"bool_trait_(un)def" headers [boost/type_traits/detail], which seem much 
more portable than just inheriting from a "bool holder type").

I generated a simple stress test, instantiating it for about 500 
different types and the results look very promising:

        modified version     |    original version
    GCC        13 seconds    |          5 minutes (*)
   MSVC 13 / 7(#) seconds    |        1.5 minutes

(*) the machine started swapping after gcc had ate up all
     physical memory
(#) ANSI-mode /Za

The categorization pipeline was successfully tested with
gcc 3.2, 3.3 and 3.4, msvc 13.10.3077, bcc 5.5.1, 5.6.4.

If I did not forget anything, it should be sufficient to implement 
builtin operator detection on top of it, too.
Here's a list of the leaves in the categorization inheritance graph 
(i.e. the finest level of separation):

Non object types:
   function  (function - not function pointer)
   void_type (represents void)

Each LValue and RValue of these object types:
   aggregate   (class or union)
   enumeration
   floating
   integral
   object_ptr  (pointer to object type)
   special_ptr (pointer to member, function or member function)

On MSVC (in ANSI-mode, that is) for example, it does not need a single 
Type Traits class to accomplish this.
Note that the 'is_plus_op' test uses the full categorization - so there 
is no extra cost in performance.

Regards,

Tobias

P.S.: There is a note within the Type Traits ICE workaround 
documentation about Metrowerks having problems using sizeof on the 
result type of an overloaded function (dated 2001) - is this still true 
for later / the current version ?