Objective C - KeyValuePair class?

Question

I'm looking for a class in Objective C similar to C#'s KeyValuePair (even without the generics). Just anything that has a first/second object. I can create my own with no problem, but I figure if one is already there, then there is no need to re-invent the wheel. I have not had any luck findind one myself... Does anyone know of one?

Answer 1

What about using plain C structs? It's "quicker" than writing an entire class.

typedef struct KeyValuePair {
     const char *key;
     const char *value;
} KeyValuePair;

//init like this
KeyValuePair kvp = {"yourkey", "yourvalue"}

Things to keep in mind:

• Structs are passed by value.
• ARC prevents using ObjC objects with structs but C primitives are still supported.
• You cannot add structs to ObjC collection classes (NSArray, NSDictionary, etc).

Answer 2

How about a simple NSArray?

NSArray* kvp = [NSArray arrayWithObjects: key, value, nil];
// or, using boxed literals,
NSArray* kvp = @[key, value];
...
NSObject* key = [kvp firstObject];
NSObject* value = [kvp lastObject];

You could make a function to wrap +arrayWithObjects: (and handle the case of a nil key or value which would trip up the simple approach)

Accessing the elements of an NSArray will probably be quicker than an NSDictionary.

Answer 3

So basically like a hashmap, right?

Use NSMutableDictionary

Example from here:

NSMutableDictionary *dictionary = [[NSMutableDictionary alloc] init]; 

// Add objects to a dictionary indexed by keys

[dictionary setObject:@"A Book about the Letter A" forKey:@"A"];
[dictionary setObject:@"A Book about the Letter B" forKey:@"B"];
[dictionary setObject:@"A Book about the Letter C" forKey:@"C"];

// Retrieve an object from a dictionary with a key

NSLog([dictionary objectForKey:@"B"]);

// Release a dictionary

[dictionary release];