In my last post, I compared the collections classes at a high level. Now I’m diving into the one that is most often used, the OrderedCollection.
What’s an OrderedCollection? It is the collection class in Smalltalk that supports ordering. Seems straightforward, but why use the Smalltalk name for it? Why not the more popular List or Array? Because Smalltalk and its collection classes have been around for much longer (over 25 years) than the other languages I’m comparing. All the other languages actually derive in some fashion from Smalltalk.
I haven’t done that much Python and C#, but I figured I should check them out while I am at it. For the others, I have done quite a bit and I wanted to take a step back and look at how each compares.
Here’s a table that compares the API for each language:
(Note that I’ll use “list” since it is shorter than “OrderedCollection” so it can fit nicely in this table.)
||List – ArrayList
||NSArray / NSMutableArray
||IList – List
|list := OrderedCollection new
||List<Type> list = new ArrayList<Type>()
||NSMutableArray *list = [NSMutableArray array];
||list = Array.new or list = 
||list = 
||IList list = new List();
|list add: item
||[list addObject: item];
|list addAll: anotherList
||[list addObjectsFromArray: anotherList];
||list = list + another_list
|list remove: item
||[list removeObject: item];
|list indexOf: item
||[list indexOfObject: item];
|list includes: item
||[list containsObject: item];
||item in list
|list at: index
||[list objectAtIndex: index];
||list.at(index) or list[index]
Now I’m going to argue against using Array as a name, because people tend to confuse it with C-style arrays. Most of these languages can interface with C (usually to optimize certain sections of code or to interoperate with legacy libraries) and so it is nice to not have two concepts referred to via the same name. So ideally I’d like to see Ruby change Array to List and Obj-C/Cocoa use NSList and NSMutableList. I doubt I will make this happen, however. :)
Next, more heresy: Java and C# have backwards syntax for constructors. Why don’t they just make it like every other method call and have a “new” method at the class level like every other language? (Not sure if Python’s List is actually a class.) Hmm… maybe someone can contribute this for Java 6?
Nobody seems to agree on a method name for size, count, or length. Note that Python doesn’t seem to have a method for this, rather a len() function. Also Python doesn’t have an includes: method, but an “in” language operator.
Java seems to mirror Smalltalk nicely, with a few wording changes and a C++-like syntax. I included the type-safe Java 5 syntax for the Java constructor to show how it makes life a bit safer with compile-time type safety, but also clutters the code a bit to accommodate the type. Note that this clutter is saved later when you get rid of casts.
Objective-C also mirrors Smalltalk, but seems to add “Object” everywhere, making them verbose. I wouldn’t mind if this got replaced by a more bare protocol later on.
Actually, Obj-C has a language feature called “categories”, which lets you extend an existing class without creating a subclass. So does Ruby and possibly Python. Java does not let you do this. Not sure of C#. I think I will try and see if creating and using a new Obj-C category and Ruby mix-in that lets me use the Smalltalk-canonical method names will be easier, since I will only have to remember one set of method names.
Note also that Objective-C has to wrap method calls in square brackets.
Also Objective-C (actually Cocoa’s Foundation Kit) has both an immutable and a mutable version. The immutable version gives you thread-safety and is faster. I addressed this in the earlier post about collections. Note that Java’s ArrayList is not thread-safe by default.
Ruby has an interesting convention of using ? at the end of its method names instead of using “is” and camel-casing. Note that camel-casing is discouraged in Ruby. Instead, the preferred Ruby convention is a_long_method_name instead of aLongMethodName. It also seems to be derived from Python as well as Smalltalk, but is more object-oriented. While it has the  operator like Python, it uses methods instead of len() and the keyword in.
C# looks just like Java. Note that C# 2.0 has Generics support, like Java 5. The only thing that is odd is that it uses a different casing model, with the first letter of the method name uppercased.
Next: iterating over OrderedCollections.