Mark Needham

Thoughts on Software Development

Objective C: Observations

with one comment

I’ve been playing around with Objective C over the last month or so and although my knowledge of the language is still very much limited I thought it’d be interesting to describe some of the things about the language that I think are quite interesting and others that keep catching me out.

Protocols

I touched on protocols a bit in my first post but they seem like an interesting middle ground between interfaces and duck typing.

I like the fact that protocols can define optional methods so that if we’re not interested in some parts of the protocol we can just ignore those parts.

From the documentation page:

Protocols free method declarations from dependency on the class hierarchy, so they can be used in ways that classes and categories cannot. Protocols list methods that are (or may be) implemented somewhere, but the identity of the class that implements them is not of interest. What is of interest is whether or not a particular class conforms to the protocol

Smalltalkish style method names

We played with Smalltalk in a coding dojo a bit last year and the first thing that I noticed with Objective C is that the method names are very similar to those in Smalltalk.

I think this influences the way that we define the method name and its parameters as you try and define those in such a way that when you call the method it will read better.

For example I created the following method:

UILabel *aLabel	= [self createLabelFrom:project withXCoordinate:x withYCoordinate:y];

If I didn’t have to name the parameters when calling the method I doubt I would have used such descriptive names. I would have just used ‘x’ and ‘y’ as the names!

All methods are public/Defining methods in header files

As I understand it all the methods defined on an object are available to any other object to call i.e. all the methods are public

I’ve read about others using categories to simulate the idea of having non public methods but I haven’t tried anything myself yet.

Interestingly we get a compiler warning when trying to call methods on an object if those methods haven’t been defined in the appropriate header file although the code still seems to execute fine at run time.

Messages not method calls

One other thing that I sometimes forget is that we’re dealing with messages rather than method calls.

We still need to send the message to ‘self’ even if it’s a message being sent to another method on the same object.

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Written by Mark Needham

August 31st, 2010 at 6:27 pm

Posted in Objective C

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  • bob

    “but they seem like an interesting middle ground between interfaces and duck typing.” How do you think they are *different* from interfaces?