Re: Compile-time polymorphism of "interfaces"

From:
xucaen <xucaen@gmail.com>
Newsgroups:
comp.lang.c++.moderated
Date:
Thu, 19 Jul 2007 09:59:43 CST
Message-ID:
<1184852772.367835.295810@e16g2000pri.googlegroups.com>
On Jul 18, 3:13 pm, Andrew Schweitzer <anschweit...@gmail.com> wrote:

Compile-time polymorphism newbie question here. We are using virtual
functions and getting a performance hit in a device driver. Can some
suggest a way to implement this with templates? We don't actually need
run-time polymorphism, but we do want to share a bunch of code at
compile time.

class IInterface1{public: virtual void DoSomething() = 0;};

class IInterface2{public: virtual void DoSomethingElse() = 0;};

class Dervied1 : public virtual IInterface1{
    int m_i;
    IInterface2* m_pII2;
public:
    virtual void DoSomething() {m_i++;}
    void UseInterface(){m_pII2->DoSomethingElse();}

}

class Dervied1v2 : public virtual IInterface1{
    int m_i;
    IInterface2* m_pII2;
public:
    virtual void DoSomething() {m_i++;}
    void UseInterface(){m_pII2->DoSomethingElse();}

}

class Dervied2 : public virtual IInterface1{
    int m_i;
    IInterface1* m_pII1; //Might be a Derived1 or a Derived1v2, but it
would be nice
                                //to figure out at compile time and
get rid of virtual.
public:
    virtual void DoSomethingElse() {m_i++;}
    void UseInterface(){m_pII2->DoSomething();}

}

The ways I thought of to do this with templates all seemed to have
circular definitions.

Thanks,

Andy

--


Hi, this looks like you are trying to implement the Adaptor pattern.
I'm wondering if you tried something like:

template<typename T>
class Dervied1 : public virtual IInterface1{
    int m_i;
    T* m_pII2;
public:
    virtual void DoSomething() {m_i++;}
    void UseInterface(){m_pII2->DoSomethingElse();}

}

This class implements Interface1, then at compile time, T becomes any
other object which implements any other interface which contains the
methods you are expecting. If T is a class which does not contain the
methods you expect, this will be a compile time error instead of a run
time error.
Google "c++ adapter pattern template" brings back many examples.
http://www.google.com/search?hl=en&q=c%2B%2B+adapter+pattern+template&btnG=S
earch

Hope this helps..

Jim

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