Possible to define BaseClass functions where derived's have diff. return type/args?

**6tr6tr** · 04-17-2008

I want to create a base class that tells people that there will be two methods but not specify what the args or return type are. How would I do this?

Code:

//Something along the lines of
template <typename T>
class Test
{
public:
         T load(SomeClass a);
         void save(SomeClass a, T b);
};

class DerivedA : public Test
{
public:
         File load(SomeClass a);
         void save(SomeClass a, File b);
};

class DerivedB : public Test
{
public:
         Text load(SomeClass a);
         void save(SomeClass a, Text b);
};

Is that valid? is there a better way?

**Sebastiani** · 04-17-2008

>> Is that valid?

you have to pass the type to the template, eg:

class DerivedA : public Test<File>

>> is there a better way?

possibly. without a more detailed example it's difficult to say, though.

**6tr6tr** · 04-17-2008

Thanks. One related question:

In Java if you have a class (or interface) defintion, you can create a class on the fly without having to predefine it. Is this possible in C++?

Code:

//If I have interface DataObject
class Some
{
private:
     PrivateClass d;

public:
     DataObject get()
     {
          return new DataObject()
          {
                public getData()
                {
                     return d.data();
                }
          };
     }    
};

**laserlight** · 04-17-2008

In Java if you have a class (or interface) defintion, you can create a class on the fly without having to predefine it.

What do you mean? Perhaps you have a Java example?

**Elysia** · 04-17-2008

Note that C++ does not support get/set. You have to create your own functions or use a specialized homebrewn class for that.
Also note that you can't use classes or types which have not yet been defined (you must have the proper definition before you can use the type or class).

**6tr6tr** · 04-17-2008

Originally Posted by laserlight

What do you mean? Perhaps you have a Java example?

Code:

interface ActionListener
{
       public void actionPerformed(ActionEvent e);
}

class Test
{
       public ActionListener getListener() 
       {
              //This returns an object that is of class type ActionListener 
              return new ActionListener() 
              {
                      public void actionPerformed(ActionEvent e) 
                      {
                             // do something 
                      }
              };
        )
}

**Sebastiani** · 04-17-2008

the closest thing we have to that is lambda functions.

**CornedBee** · 04-17-2008

C++ has local classes, but they're pretty much useless. It doesn't have anonymous local classes like Java.

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