CODEWITHSUNDEEP
objective-cnsdictionary
Martin Van Nostrand
Martin Van Nostrand

Reputation: 161

Why should I not be using [NSDictionary objectForKey:]?

I recently started using Faux Pas (http://fauxpasapp.com/), and for my project I get the following warning a number of times:

Old, verbose Objective-C syntax

-[NSDictionary objectForKey:] is called. Consider using an Objective-C subscript expression instead.

I'm unsure what the subscript expression is, and I'm not having much luck finding anything on it. I was curious if anyone here could help.

Thanks!

Upvotes: 1

Views: 2269

Answers (3)

user3078856
user3078856

Reputation:

Well typically you would have written something like this:

NSDictionary *dictionary = [NSDictionary dictionaryWithObject:[NSNumber numberWithInteger:42] forKey:@"foo"];
id value = [dictionary objectForKey:@"foo"];

And now you would write something like this:

NSDictionary *dictionary = @{@"foo": @42};
id value = dictionary[@"foo"];

Which, I think you will agree is a lot simpler and nicer to look at.

Some nice information about Object Subscripting can be found at NSHipster

Upvotes: 4

matt
matt

Reputation: 536026

You want to learn about Objective-C 2.0. The best way is to go straight to the source:

http://clang.llvm.org/docs/ObjectiveCLiterals.html

As you can see, a number of language features were introduced: NSNumber literals and "boxing" expressions, along with subscripting of NSArray and NSDictionary (and your own classes if you like). This is considered the "modern" way.

Xcode will refactor your code into "modern Objective-C" for you (see under Edit > Refactor), so you can modernize your code without doing any work!

Upvotes: 2

zaph
zaph

Reputation: 112873

There is no performance difference, just that the literal syntax is more clear, less verbose and has been available for several years now.

If the current code is like:

id var = [dictionary objectForKey:@"key"];

replace it with:

id var = dictionary[@"key"];

Upvotes: 6

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