----- Original Message ----- From: "John Maddock" <[EMAIL PROTECTED]> To: "Boost mailing list" <[EMAIL PROTECTED]> Sent: Wednesday, November 13, 2002 8:53 AM Subject: Re: [boost] Can type_traits be user specialized?
> > Suppose I'm writing some generic piece of numeric code that can be > > instantiated with a User Defined Type (UDT). > > And further suppose that I need to detect whether the generic numeric type > > represents either integer or floating point values. > > Can I use type_traits is_integral<> (or is_float<>)? That is, is the user > > allowed to provide her own specializations of this templates? > > If not, how should I let the user tell whether her numeric UDT is > > integer/float/signed/etc...? > > No, is_integer and is_float etc are for built-in types *only*. If you want > to detect UDT's that are pretending to be numbers, then you should use > std::numeric_limits<>, and provide a specialisation for these if required. > > John Maddock > http://ourworld.compuserve.com/homepages/john_maddock/index.htm > Thanks, that's what I thought. I have a problem however, which I think it would be useful to discuss generally. Unfortunately, some compilers -like bcc55- provide a 'default' numeric_limits<> with no compile-time constants, while the specializations do have compile-time values. Therefore, boost's numeric_limits<> is not picked up for these compilers; but trying to use numeric_limits<> with user defined types fails to compile unless the types explicitly specialize it properly. I see three possible solutions here: (1) REQUIRE user defined types to *properly* specialize numeric_limits. (2) Enhance boost/limits.hpp so that it 'fixes' only the default numeric_limits<> if only that one is broken. (3) Define my own user specializable traits. (3) is IMO a very bad idea since we would end up with overlapping traits and potential ODR violations. (2) might be a better solution but requires further examination. (1) is the easiest way to go from the library developer POV, but might annoy users. What's your advise? TIA, Fernando Cacciola _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
