Re: Can we use abstract class templating classes?

From:
"newbie" <mitbbsmj@yahoo.com>
Newsgroups:
comp.lang.c++
Date:
16 Mar 2007 16:49:59 -0700
Message-ID:
<1174088999.440526.78970@e65g2000hsc.googlegroups.com>
On Mar 16, 4:37 pm, "Jim Langston" <tazmas...@rocketmail.com> wrote:

"newbie" <mitbb...@yahoo.com> wrote in message

news:1174087889.837628.126750@n59g2000hsh.googlegroups.com...

Say I have the following class:

class MyAbs {
 virtual ~MyAbs() {}
 virtual void foo() = 0;
 virtual void bar() {cout << "abs::bar"; }
}

class MyDer1: public MyAbs {
 MyDer1() {counter = 0; }
 foo() { cout << "der1::foo--" << counter++; }
 int counter;
}

class MyDer2: public MyAbs {
 MyDer1() {counter = 100; }
 foo() { cout << "der1::foo--" << counter--; }
 int counter;
}
-----------------------------------------
Can I do something like this? Thanks

template <class Toy>
class MyTemplateClass{
 Toy toy_;
 Play() { toy_.foo(); }
}


Your code shows classes MyAbs, MyDer1 and MyDer2, yet your template shows
Toy. I'm presuming in my response that by
Toy toy_;
Play() ( toy_.foo(); )

you actually meant
MyAbs toy_;
Play() { toy_.foo(); }

No. Your template is attempting to instantize a class MyAbs which is a
virtual class. You couldn't do it in main so you couldn't do it in a
template. However, I believe you could do:

MyAbs* toy_ = new MyDer1;
Play() { toy_->foo(); }


Thanks. I am not sure

What I really want is to ask class MyTemplateClass behave clever
enough to
understand things like

///////////////////////////////////
class MyAbs {
  virtual ~MyAbs() {}
  virtual void foo() = 0;
  virtual void bar() {cout << "abs::bar"; }

}

class MyDer1: public MyAbs {
  MyDer1() {counter = 0; }
  foo() { cout << "der1::foo--" << counter++; }
  int counter;

}

class MyDer2: public MyAbs {
  MyDer1() {counter = 100; }
  foo() { cout << "der1::foo--" << counter--; }
  int counter;
}
///////////////////////////////////////

template <class Toy>
class MyTemplateClass{
  Toy toy_;
  Play() { toy_.foo();
}

typedef MyTemplateClass<MyDer1> MyClass1;
typedef MyTemplateClass<MyDer2> MyClass2;
////////////////////////////////////////
int main() {
  MyClass1 m1;
  MyClass2 m2;
  m1.Play();
  m2.Play();
  return 0;
}

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