Objective-C has good aspects like lightweight syntax that extends C, dynamic message sending without inheritance, and true introspection. It allows adding methods to classes through categories and proxies. Key-value coding and binding facilitates runtime binding of object properties. However, it also has drawbacks like verbose syntax with square brackets, lack of language support for non-message sending code, and half-manual memory management without garbage collection. While frameworks like Cocoa mitigate issues, Objective-C trades type safety for runtime features.

1. Objective-C: Good and Bad

2. Good

3. Lighweight
Simply preprocessor and small runtime
Syntax sugar over C, easy to learn

4. Runtime
Completely dynamic message sending.
Don't need inheritance to call a method
with different objects
True introspection. Allows to watch class
hierarchy, check if an object has a
particular invariant or implements some
method, call a method by name

5. Categories and Proxies
Allows addition of methods to another class
Even a class you don't have source for
Also allows overriding of existing methods

6. Key Value Coding/Observing
Bind string names with object invariants at
run-time
Call back when the value of some invariant
is going to be / was changed

7. Self-contained objects
Objects tend to be handful and smart
enough to be used standalone

8. #import
No include guards or “#pragma once”
anymore

9. [NSBundle classNamed]
Create a class by name, which could be
used later to instantiate objects

10. Blocks
Closures are awesome
Allows to define a block of code with
surrounding context and pass it to other
function
Facilitates concurrency

11. Bad

12. Syntax
Lots of square braces. Compare:
[[[MyClass alloc] init:[foo bar]] autorelease]
MyClass.alloc.init(foo.bar).autorelease
Keyed parameters: difficult to reorder them
during refactoring

13. Lighweight
The same code has to be repeated often
Little language support for anything other
than message sending
Folks could say “because there's no magic”.
But more code means more bugs
Without Cocoa this “no magic” would be
absolutely awful

14. Memory Management
Half-manual, half-automatic
Raw pointers are evil
No garbage collector
Reference counters overhead
Migration to automatic reference counting
takes time

15. Allocation and Initialization
Which are two separated operations
MyClass *object = [MyClass alloc] init];
Multiple constructors work via designated
initializers without any language support
self = [super init]; //assignment to self :(
if (self)
{
//init invariants
}
return self;

16. No Stack Objects
Dealloc won't be called automatically

17. Messaging nil
Does nothing and hides real bugs
Wouldn't be so bad if it were easy to make
messaging nil scream
Cocoa messages nil as a matter of course

18. Overriding and Overloading
Categories are broken: overriding a method
more than once leads to undefined
behavior
No method overload. Need to mangle
names manually

19. No Namespaces
Not a major gripe, but It's real handy

20. Id should be id *
Not clear:
NSString *foo = @”foo”;
id bar = foo;
Better:
NSString *foo = @”foo”;
id *bar = foo;

21. So So

22. Frameworks
Could be a problem, if Cocoa wasn't the
best one publicly available

23. Type Safety
Can't catch lots of errors during the compile
time
But allows its awesome runtime features

24. Questions?