Can Type be Redefined in Inherited Class?

[eoneuk]

In the following simple example, I want to redefine z so that in class c it is an integer, and in d, a real.  When I compile I get an error message "duplicate identifier z". 

Can this be accomplished, and if so, how?

Ed

Code: [Select]

type
  c = class
 type
    z = integer;
  var
    x,y : z;
  end;

  d = class(c)
  type

    z = real;

 end  ;


[Blaazen]

Try to make it private.

[eoneuk]

Thanks for your reply, but making it private had no effect.

Ed

[marcov]

No, this is not possible.

[Blaazen]

It is possible (with type defined in private section), but descendant class has to be in other unit.

[eoneuk]

Placing the descendant class in another unit, resolved the compiler error.
However, when using the classes in a program, z is not redefined in class d, but is the same as whatever is defined in class c. 

Are there any additional statements needed to make this work?

Ed

[Blaazen]

And what are you trying to achieve? You can define type with the same name (z) in each class but that doesn't change the fact that pascal is statically typed language, so whatever method working with type "z" will have to be reintroduced.

[marcov]

It is possible (with type defined in private section), but descendant class has to be in other unit.

It is not possible to redefine it, only to define a different type, but with the same name in a different scope. Which is probably not a solution.

Generic types are, and can be inherited, but in Delphi generics, you can do nearly no operations on a generic type T. (since there is no constraint modifier for ordinal or real types)

[Mike.Cornflake]

Thinking about a possible redesign of your class, would an overloaded function GetValue solve your problem?  Each descended class stores the value in it's own internal variable, and each descended class exposes an overloaded GetValue of the appropriate datatype?  (just ensure you don't declare your original GetValue as virtual, and I think this is doable)

Only other workaround I think of was for you to use Variants instead a static type.  Introduces memory overheads though...

[eoneuk]

I was able to accomplish my goal by the use of variants.

Thank all of you for your timely replies and suggestions.  This is a great forum!


Ed

[User137]

I guess the solution is to not declare x,y : z; in the class C at all. Since type Z is not known yet, C is just a abstract class.