Comments on: Adding firstObject to NSArray

By: Dave

Dave — Mon, 15 Nov 2010 23:13:58 +0000

Kent Beck in his implementation patterns book talks about symmetry, matching levels of abstractions throughout your code, so if there’s a lastObject, it makes sense there should be should be a firstObject too. There have been edge cases when I’ve used [array objectAtIndex: 0] in certain situations during coding and thought it was ‘ugly’ and didn’t fit in with the level of abstraction in my code at the time; perhaps it’s a style thing, a level-of-abstraction thing, who knows – maybe there should be methods [array head] and [array tail]

By: Foo

Foo — Sat, 10 Apr 2010 19:06:02 +0000

@Jill:

Well, at first glance your statement appears to be valid.
Yet upon further inspection you should notice a subtle difference between

[array objectAtIndex:0];
[array firstObject];

Try to run those two on an empty array.
Result: The former method will throw an exception whereas the latter (category) method does not, returning nil instead. Just like Apple’s “[array lastObject]” uses to do it.

Summing up: [array objectAtIndex:0] != [array firstObject] and by that in no way “pointless”.

By: Jill

Jill — Mon, 22 Feb 2010 04:00:56 +0000

There’s a reason there’s no “firstObject”: It’s not needed.
Object #0 *ALWAYS* is the 1st object.

Doing all that extract/unneeded work… to create your own firstObject is like saying:
The first book on that shelf is the first book.

Your code is an excellent example of “categories”… but used in a pointless way.

“Category” is a VERY powerful thing. Use it as such.