Do you use constants when working with NSDictionary?

Question

I understand using constants for your names in a NSDictionary to prevent typos (myName will auto complete vs @"myName" won't).

i'm working with a medium size dictionaries right now and a couple of times, i've misstyped key names and had to spend some time tracking down where i miss spelled a word.

i'm wondering, do you consider it worth while to set up a constants naming scheme?

Yes, if you use them a lot. It also makes refactoring (err, renaming the keys) easier. — Costique, Feb 10 '12 at 17:28

score 21 · Accepted Answer · answered Feb 10 '12 at 17:34

Yes, but I'd advise defining proper string constants rather than #defines for your strings because string constants are type-safe and every reference will use the same actual string object, which improves the performance of using isEqualToString: to compare them.

To define a private string constant you can put this in your .m file:

static NSString *const MyConstant = @"MyConstant";

To make it public, you can either put this in your .h file instead, or you can split the definition by putting this in your .h:

extern NSString *const MyConstant;

And this in your .m file:

NSString *const MyConstant = @"MyConstant";

+1 very good answer and totally the way to go -- hopefully this will be read by some of my coworkers who are constantly using defines for those things; thunder and lightning shall hit them on the toilet! — Till, Feb 10 '12 at 21:18

score 4 · Answer 2 · answered Feb 10 '12 at 17:29

4

I usually create a GlobalDefinitions.h file and place macros that I can use in code instead of magic strings.

.h file

#define PERSON_NAME @"Person_name"
#define PERSON_BDAY @"Person_bday"

By including the .h file you can now access you values like so

[dictionary objectForKey:PERSON_NAME];

answered Feb 10 '12 at 17:29

Joel Kravets

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Note that constant string are better than #def'd strings. See http://stackoverflow.com/questions/538996/constants-in-objective-c – Matt Wilding Feb 10 '12 at 17:34
Agreed - see my answer below for how to define string constants. – Nick Lockwood Feb 10 '12 at 17:34

score 3 · Answer 3 · answered Feb 10 '12 at 17:27

3

Yes, it's worth it. Consistency in something like this does what you say: it cuts down on errors and saves you time.

answered Feb 10 '12 at 17:27

Rayfleck

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Do you use constants when working with NSDictionary?

3 Answers3