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List:       kde-multimedia
Subject:    More MSOP stuff: dynamic casting and aliasing
From:       Nicolas Brodu <nicolas.brodu () free ! fr>
Date:       2000-05-14 19:44:13
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Hi all,

I've also written dynamic casting and aliasing this WE. What it is:

Dynamic casting:

Suppose you have interface A : B {};
You can write
  B b;
  A a = b;  // True as for standard C++ pointers
But now if you do
  Object o = a;
You know that the object is a B, but cannot assign it to a B variable.

Now you can, by writing:   B bb = DynamicCast(o);

If the cast wasn't possible, bb.isNull() will be true.


Aliasing:

This is very similar in functionalities to Stefan virtual ports, in the sense
that it provides masquarading and dynamic composition. Since Stefan complained
in the TODO about the virtual ports, I felt free to write something different.

Example: You have some effect filters, and would like to group-chain them and
treat the result as a single filter object. It is now possible. Supposing all
Effects have an "input" and an "output" port:
  Effect e, f, g;
  connect(e,f);
  connect(f,g);  // That makes the chain of effect
  Object group;
  alias(group,"input",e,"input"); // this create a port name "input" in group
  alias(group,"gout",g,"output");  // and another named "gout" (for a change)
Now if you have
  DataProducer d;
  Player p;
You can do
  connect(d,group,"input");  // In fact connect d to e
  connect(group,"gout",p); // and g to p

group has become a single object that calls in fact the 3 others, transparently. 

You'll find all this here again:
  http://nicolas.brodu.free.fr/arts.tar.bz2

That's all, folks!
Nicolas
-- 
A shortcut is the longest distance between two points. (unknown author)
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