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Mix Static and dynamic Polymorphism
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Jun  
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 More options 7 Nov, 15:16
Newsgroups: comp.lang.c++.moderated
From: Jun <junh...@gmail.com>
Date: Sat, 7 Nov 2009 09:16:28 CST
Local: Sat 7 Nov 2009 15:16
Subject: Mix Static and dynamic Polymorphism
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Hello all,

I just tried to mix static and dynamic polymorphism together.

I've a vector to store all the elements, and the implementations
of elements are slightly different. I used Policy-based design:

struct Interface{
   virtual void run(void) = 0;
   virtual void execute(void) = 0;

};

struct PolicyA{
   void execute(){
      // implementing Policy A;
   }

};

struct PolicyB{
   void execute(){
      // implementing Policy B;
   }

};

template <class Policy>
struct Base : public Policy, public Interface{
    void run(){
         // implementing base ;
    }

}

Anyway, those codes don't compile ....  Anyone has some suggestions ?
Thank you in advance.

Jun

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Neil Butterworth  
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 More options 7 Nov, 21:22
Newsgroups: comp.lang.c++.moderated
From: Neil Butterworth <nbutterworth1...@gmail.com>
Date: Sat, 7 Nov 2009 15:22:44 CST
Local: Sat 7 Nov 2009 21:22
Subject: Re: Mix Static and dynamic Polymorphism
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With the addition of a semicolon to the end of the Base struct:

template <class Policy>
struct Base : public Policy, public Interface{
   void run(){
     // implementing base ;
   }

};

your code compiles for me with g++ 4.4.0. What compilation errors are
you getting?

Neil Butterworth

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Jun  
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 More options 8 Nov, 00:23
Newsgroups: comp.lang.c++.moderated
From: Jun <junh...@gmail.com>
Date: Sat, 7 Nov 2009 18:23:17 CST
Local: Sun 8 Nov 2009 00:23
Subject: Re: Mix Static and dynamic Polymorphism
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{ Please avoid top-posting, and don't quote the clc++m banner. -mod }

Hello all,

I just reach a solution that simply regard interface::execute as a
wrapped member function,
name it different from PolicyA::execute and wrap it inside:

struct Interface{
     virtual void run() = 0;
    virtual void executeInterface() = 0;

}

template <class Policy>
struct Base : public Policy, public Interface{
    using Policy::execute;
     void run(){
          // implementing base ;
     }

    void executeInterface(){
         execute();
    }

}

This solution is just a little bit "ugly", could someone find a
solution
that compose the Interface class ? Thank you in advance.

Jun

On Nov 7, 11:16 am, Jun <junh...@gmail.com> wrote:

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tohava  
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 More options 8 Nov, 00:24
Newsgroups: comp.lang.c++.moderated
From: tohava <toh...@gmail.com>
Date: Sat, 7 Nov 2009 18:24:14 CST
Local: Sun 8 Nov 2009 00:24
Subject: Re: Mix Static and dynamic Polymorphism
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On Nov 7, 5:16 pm, Jun <junh...@gmail.com> wrote:

> Anyway, those codes don't compile ....  Anyone has some suggestions ?
> Thank you in advance.

First, it would be wise to include the compilation errors.
Second, I'd recommend rewriting as:

struct Interface{
    virtual void run(void) = 0;
    virtual void execute(void) = 0;

};

struct PolicyA : public Interface {
    void execute(){
       // implementing Policy A;
    }

};

struct PolicyB : public Interface {
    void execute(){
       // implementing Policy B;
    }

};

template <class Policy>
struct Base : public Policy {
     void run(){
          // implementing base ;
     }

}

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Maxim Yegorushkin  
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 More options 8 Nov, 00:24
Newsgroups: comp.lang.c++.moderated
From: Maxim Yegorushkin <maxim.yegorush...@gmail.com>
Date: Sat, 7 Nov 2009 18:24:34 CST
Local: Sun 8 Nov 2009 00:24
Subject: Re: Mix Static and dynamic Polymorphism
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On 07/11/09 15:16, Jun wrote:

You could try inheritance chaining:

   struct Interface {
      virtual void run() = 0;
      virtual void execute() = 0;
   };

   template<class Itf>
   struct PolicyA : Itf {
      void execute() {
         // implementing Policy A;
      }
   };

   template<class Itf>
   struct PolicyB : Itf {
      void execute() {
         // implementing Policy B;
      }
   };

   template<class Policy>
   struct Base : Policy {
       void run(){
            // implementing base ;
       }
   };

   typedef Base<PolicyA<Interface> > BaseA;
   typedef Base<PolicyB<Interface> > BaseB;

   int main()
   {
       Interface const& a = BaseA();
       Interface const& b = BaseB();
   }

--
Max

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Bart van Ingen Schenau  
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 More options 8 Nov, 15:52
Newsgroups: comp.lang.c++.moderated
Follow-up To: comp.lang.c++.moderated
From: Bart van Ingen Schenau <b...@ingen.ddns.info>
Date: Sun, 8 Nov 2009 09:52:22 CST
Local: Sun 8 Nov 2009 15:52
Subject: Re: Mix Static and dynamic Polymorphism
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Because PolicyA and Interface are two unrelated classes, the
PolicyA::execute() member will never be considered and overrider for
Interface::execute().

> struct PolicyB{
>    void execute(){
>       // implementing Policy B;
>    }
> };

> template <class Policy>
> struct Base : public Policy, public Interface{
>     void run(){
>          // implementing base ;
>     }
> }

Base<T> remains an abstract class, because it does not have an overrider
for the pure-virtual member execute() that was inherited from Interface.
The most likely solutions are:
1. Add another member to Base, to connect the two inherited execute()
functions:
   template <class Policy>
   void Base<Policy>::execute(){
     Policy::execute();
   }
2. Change the inheritance hierarchy such that the policy classes inherit
from Interface.

> Anyway, those codes don't compile ....  Anyone has some suggestions ?
> Thank you in advance.

> Jun

Bart v Ingen Schenau
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