Categories allow you to add functionality to already existing classes without extending them.
ideone.com/NsuFP is a complete example comprising of an interface implementation, allocate, initialize,method invocation
[obj morebar: 250] is how you would invoke a method morebar which takes a parameter int on the object obj.
id obj = [[foo alloc] init]; will allocate and initialize an object of type foo
All instance variables are private in Objective-C by default, write getters and setters Use @synthesize directive to autogenerate these
All Objective-C object variables are pointers types. The id type is predefined as a pointer types, sort of like your void *
- before a method name means it's an instance method. + before a method name means it's a class method.
nil object is the functional equivalent of the null pointer without the crashing part
The implementation of these methods is stored in <classname.m> e.g., foo.m. You could define methods in foo.m but is considered unsupported
The class interface is usually stored in a file <classname.h> for instance, foo.h and defines instance variables and public methods
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