Need create and call method from many class types

[WojTec]

Hello, guys,

So, lets say what I have.

I have two classes:
- TClass1(TBaseClass)
- TClass2(BaseClass)

TClass1 and TClass2 extands TBaseClass, both are for different input data types. TClass1/TClass2 has LoadFromStream and SaveToStream.

Now, how to create and call methods with names that are common for any class TSomeOtherClass(TClass1/TClass2), like stream procedures?

Currently I have:

if class = someclass then someclass.loadfromstream
else if class = otherclass then otherclass.loadfromstream
else if class = yetanotherclass then yetanotherclass.loadfromstream

but in future I'll have too many classes to add if statement in few places in few units in program.

Could you help with this?

[mkinzler]

Why not if class is TBaseclass then BaseClass( class).loadfromstream()); ?

[WojTec]

And this will call correct method (someclass.loadfromstream)?

[mkinzler]

Yes, if BaseClass is a superclass of class

[WojTec]

What it mean? This is somethink like this (I saw somewhere, but don't know how it working):

TClassOfBase = class of TBaseClass

Delphi-Quellcode:

TBaseClass = class;
TSomeClassA = class(TBaseClass);
TSomeClassB = class(TBaseClass);

//(TSomeClassA and TSomeClassB) are base for any class I'm working with it).

I have TClass1(TSomeClassA), TClass2(TSomeClassB), etc. How it should be done to avoid many thousends if-then-else?

Could you explain me, because I don't understand?

[mkinzler]

Because of the IS-A paradigm each Subclass "is a" Baseclass

if the wanted function/procedure is declared in a superclass ( baseclass->MiddleClass->Class1) it can be called as function/procedure of the superclass. It'S always called the "best matched" function.
if the function is implemented in the Baaseclass this function is called, if the implementation is in Class1/Class2 then the corresponding versions are used:
TBaseClass(class1).AnyFunc() calls Tclass1.AnyFunc()

[Aphton]

If you want to figure out how the "Class of Class" thing works, just try to understand the TPicture.LoadFromFile method, which can be found in the "graphics" unit.

[Stevie]

TBaseClass has to have LoadFromStream as virtual (abstract).