Filip Konvi?ka ha escrito:

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If you're using Boost 1.34, then you can simply use

hashed_unique< tag<userid>, member >

Hi,

I'm just curious - is there a reason why "member" takes 3 template parameters, and not just one, like in

member<&Peer::userid>

? The first two types can be extracted from the member pointer, so I find this a bit redundant...

It certainly looks redundant, but it turns out you really cannot do what you propose: template<...> struct member; What should "..." look like? It's not a type parameter, but it cannot be made a non-type parameter either since we don't know the type of the pointer-to-member being passed... In decltype- (or typeof-) enabled compilers a terser syntax could be achieved by using some macro hackery: template struct member; #define MEMBER(PtrToMember) \ member So maybe when C++0x arrives we can take advantage of this. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

Filip Konvi?ka ha escrito: [...]

I use this template in my code:

template<typename T> struct get_pointer_to_member_details;

template struct get_pointer_to_member_details { typedef Class class_type; typedef Member member_type; };

Using this, you can write (and I do) something like

template<typename MemberPointerType> struct member { MemberPointerType pMember; typedef typename get_pointer_to_member_details<MemberPointerType>::class_type class_type; typedef typename get_pointer_to_member_details<MemberPointerType>::member_type result_type;

member(MemberPointerType pMember) : pMember(pMember) {} // ... }

I wonder then, is it MSVC 8 that allows something non-standard, or is it OK? I think I tried with recent gcc as well and it worked...

Your code is fine, but it does not do what boost::multi_index::member is meant to do, namely accepting the pointer-to-member as a template parameter --rather, you're taking it as a runtime variable in construction time. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo

Filip Konvi?ka ha escrito:

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Filip Konvi?ka ha escrito: [...]

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I use this template in my code:

template<typename T> struct get_pointer_to_member_details;

template struct get_pointer_to_member_details { typedef Class class_type; typedef Member member_type; };

Using this, you can write (and I do) something like

template<typename MemberPointerType> struct member { MemberPointerType pMember; typedef typename get_pointer_to_member_details<MemberPointerType>::class_type class_type; typedef typename get_pointer_to_member_details<MemberPointerType>::member_type result_type;

member(MemberPointerType pMember) : pMember(pMember) {} // ... }

I wonder then, is it MSVC 8 that allows something non-standard, or is it OK? I think I tried with recent gcc as well and it worked...

Your code is fine, but it does not do what boost::multi_index::member is meant to do, namely accepting the pointer-to-member as a template parameter --rather, you're taking it as a runtime variable in construction time. Ah, I see...but duplicating the argument using a macro might work, like

Joaquín Mª López Muñoz (28.6.2007 9:49): this:

#define MEMBER(MemPtr) member

Umm... no, not quite so. MemPtr is a non-type parameter, so you'd have to write: #define MEMBER(MemPtr) \ member< \ get_details::class_type, \ get_details::member_type, \ MemPtr> So we have the need for a typeof-like facility agian :(

The reason why I think this is better is that when you change the member type in class declaration, you have to go through all member<> usages and change the type there too.

I agree with you having a macro like this makes usage simpler --but I haven't provided the macro because typeof or decltype is not standard and/or widely supported, and I don't know how to implement the macro without some of those. If you use GCC, which provides typeof(), then indeed you can write your private MEMBER utility in the manner described. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo