Re: [Boost-users] boost::enable_if, did I get it wrong ?

Subject: Re: [Boost-users] boost::enable_if, did I get it wrong ?
From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2009-08-18 14:21:26

You can only apply enable_if to template arguments of the function and not
of the class which contains the function, but you can't declare a virtual
function template... So this is your dilemma.

Regards,
Ovanes

On Tue, Aug 18, 2009 at 7:23 PM, topoden <_dvt__at_[hidden]> wrote:

>
> Hello,
>
> I'm trying to use boost::enable_if to customize function declaration for a
> particular set of template arguments. But instead of using SFINAE to remove
> incorrect declaration it produces error. See the example below to see
> better
> what I mean:
>
> #include <boost/utility.hpp>
> #include <boost/type_traits.hpp>
>
> template<class A, class B>
> struct BaseListener
> {
>        typename boost::disable_if<boost::is_void< B >, void>::type
>        void virtual process(A *, B *) = 0;
>
>        typename boost::enable_if<boost::is_void< B >, void>::type
>        void virtual process(A *) = 0;
> };
>
> struct Request
> {
> };
>
> struct Response
> {
> };
>
> typedef BaseListener<Response, void> BaseResponseListener;
> typedef BaseListener<Request, BaseResponseListener> BaseRequestListener;
>
> struct RequestListener : public BaseRequestListener
> {
>        void process(Request *, BaseResponseListener *)
>        {
>        }
> };
>
> struct ResponseListener : public BaseResponseListener
> {
>        void process(Request *)
>        {
>        }
> };
>
> int main(int argc, char * argv[])
> {
>        RequestListener reqListener;
>        ResponseListener resListener;
>
>        return 0;
> }
>
> error message:
> error C2039: 'type' : is not a member of 'boost::enable_if<Cond,T>'
> 1>        with
> 1>        [
> 1>            Cond=boost::is_void<BaseResponseListener>,
> 1>            T=void
> 1>        ]
> 1>
>  c:\!projects\temp\consoleeventhandler\consoleeventhandler.cpp(134)
> : see reference to class template instantiation 'BaseListener<A,B>' being
> compiled
> 1>        with
> 1>        [
> 1>            A=Request,
> 1>            B=BaseResponseListener
> 1>        ]
> --
> View this message in context:
> http://www.nabble.com/boost%3A%3Aenable_if%2C-did-I-get-it-wrong---tp25027913p25027913.html
> Sent from the Boost - Users mailing list archive at Nabble.com.
>
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