Managing collections of tuples in Objective-C

Question

I am fairly new to Objective-C and was wondering what the best way to manage collections of tuples was. In C I would use a 2D array or a struct.

Should I be creating objects to contain these tuples? It seems like overkill for just sorting lists or is there no real extra load generated by object initialisation?

Answer 1

I think you'll have to settle for an NSArray of NSArray objects, or maybe an NSArray of NSDictionary objects. You can always roll your own class, or do it the way you would do in C.

Answer 2

There are a couple different ways you could go about this:

1. CoreData. While it's not technically a database, it can behave a lot like one. If you don't need persistence between app runs, then consider using the NSInMemoryStoreType store type, as opposed to an NSSQLiteStoreType or other option. However, if you're going to want to join tuples together, using CoreData will absolutely not work (this, IMO, is the main reason why CoreData is not a database).
2. Use a real database. SQLite ships on every Mac and iPhone and is pretty easy to use if you use wrappers like FMDB or SQLite Persistent Objects or PLDatabase or EGODatabase or the GTMSQLite wrapper by Google.
3. A tuple is really just a collection of key-value pairs, so you could just use an NSMutableArray of NSMutableDictionaries. You obviously won't get to use SQL syntax, and any joins/queries you have to run yourself, but this would definitely have the easiest setup.
4. Write a tuple class and store those in an NSMutableArray (similar to #3, just enforcing a common set of attributes on your tuples).

Answer 3

There definitely is some overhead in the generation of objects. For a small number of objects, then using ObjC data structures is still appropriate. If you have a large number of tuples, I would manage them in a C array of structs. Remember, Objective-C is really just C. It is appropriate and common to use C constructs in Objective-C (to a point; learning where that point is represents a major milestone in becoming a good Objective-C developer).

Typically for this kind of data structure, I would probably create a single Objective-C object that managed the entire collection. So external callers would see an Objective-C interface, but the internal data would be stored in a more efficient C structure.

If it is common to access a lot of tuples quickly, my collection object would probably provide "get" methods similar to [NSArray getObjects:range:]. ObjC methods that begin with "get" indicate that the first parameter is a pointer that will be overwritten by the method. This is commonly used for high-performance C-like access to things managed by an ObjC object.

This kind of data structure is exactly the way ObjC developers merge the elegance and maintainability of ObjC with the performance and simplicity of C.