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Re: theoretical - Protocols

The main difference is that any class that adopts a formal protocol has to implement all of the
methods in the protocol. In that respect its like a Java interface or C++ class with pure virtual
methods. The requirement is compiler enforced.

Where it makes sense, formal protocols are to be preferred because they serve to lay out the
interaction contract in an explicit way and document for the developers exactly what is expected of the
implementors of the protocol.

It doesn't always make sense though. For instance, when doing a chain of command pattern with
delegation, you might not want to require a delegate to implement every single method you might
be able to send it. You see this most often in event handling delegation. You might want to allow the addition of a delegate that responds to keyDown: without forcing the delegate to also implement mouseDown: and all the rest of the event processing. So an informal protocol is a better choice here.

BTW, it is my opinion that informal protocols are overused by certain lazy developers.
Many of these developers write or have written library code for Apple computer.

Think it through and say what you mean when you program.

On Saturday, May 26, 2001, at 01:10 PM, Bob Savage wrote:

Hi, I'm trying to learn about protocols, but I don't quite understand
something: why are there informal protocols? It seems like the best thing
would be to use the @protocol mechanism since it exists, but even Apple
doesn't do that sometimes (e.g. "NSTableDataSource informal protocol"). Is
this just being lazy, or is there a good reason to forgo the formal protocol
definition?

Another question: IF I were to define a protocol for objects that I get from
3rd parties (via Bundles), where should I define that protocol? Right in my
".h" file for the Class that uses these 3rd party-supplied objects?

thx,

Bob
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References: 
 >theoretical - Protocols (From: Bob Savage <email@hidden>)



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