Equivalent of C++ STL container “pair” in Objective-C?

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无人及你
无人及你 2021-02-13 03:34

I\'m new to Objective-C, so please don\'t judge me too much. I was wondering: Is there an equivalent of the C++ STL pair container I can use in Objective-C?

I want to bu

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  • 2021-02-13 04:04

    How about a Pair category on NSNumber that uses associated objects, something like the code below (untested, may require iOS4 as I'm not sure when associated objects were introduced).

    #import <objc/runtime.h>
    
    @implementation NSNumber(Pair)
    
    #define PAIR_KEY 'p'
    
    - (NSNumber *) pairNumber:(NSNumber *)second
    {
        char secondKey = PAIR_KEY;
        objc_setAssociatedObject(self, &secondKey, second, OBJC_ASSOCIATION_RETAIN);
        return self;
    }
    
    - (NSNumber *) pairedNumber
    {
        char secondKey = PAIR_KEY;
        NSNumber *associatedObject = (NSNumber *)objc_getAssociatedObject(self, &secondKey);    
        return associatedObject;
    }
    
    @end
    

    You would use it like so:

    BOOL myBool = NO;
    
    NSNumber *storedBool = [NSNumber numberWithBool:myBool];
    
    [myOtherNumber pairNumber:storedBool];
    

    And to get it out:

    NSNumber *boolNumber = [myOtherNumber pairedNumber];
    
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  • 2021-02-13 04:09

    Using anonymous struct and struct literals, you might be able to do something like

    NSValue * v = [NSValue valueWithBytes:(struct {NSInteger i; bool b;}){i,b} objCType:(struct {NSInteger i; bool b;})];
    

    and then to read,

    struct {NSInteger i; bool b;} foo;
    [v getValue:&foo];
    

    It's a bit cleaner if you name your struct though.

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  • 2021-02-13 04:10

    You can write your own data structure object - for such a simple case, it would be pretty easy:

    @interface Pair : NSObject 
    {
        NSInteger integer;
        BOOL      boolean;
    }
    @property (nonatomic, assign) integer;
    @property (nonatomic, assign) boolean;
    @end
    

    And a matching implementation, then you stick your Pair objects into the NSArray problem free.

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  • 2021-02-13 04:20

    Yet another option, is to (ab)use a single-entry NSDictionary for storing the pair - since NSDictionary can now be defined to force typed "key" and "value" and also supports literals as syntactic sugar. The drawback - the pair can only hold NSObjects (instance references) and not primitive values.

    A sample would look like this:

    typedef NSDictionary<NSString *, NSDate *> *Pair;
    

    And then in your code:

    Pair myPair = @{@"my name": [NSDate date]};
    Pair myOtherPair =  @{@"his name": [NSDate date]};
    NSArray<Pair> *myArrayOfPairs = @[myPair, myOtherPair];
    

    Go on and print the results:

    NSLog(@"%@", myArrayOfPairs);
    

    and it looks very much like what you'd expect.

    2019-03-18 16:08:21.740667+0200 TesterApp[23135:23269890] (
      {
        "my name" = "2019-03-18 14:08:21 +0000";
      },
      {
        "his name" = "2019-03-18 14:08:21 +0000";
      }
    )
    

    Payback time comes as you try to extract values from the so-called "Pair". You have to actually dig that single entry from the NSDictionary, not by its "Key" as usual, but assuming there's only one entry, like this:

    Pair somePair = myArrayOfPairs.lastObject;
    NSString *name = somePair.allKeys.firstObject;
    NSDate *date = somePair.allValues.firstObject;
    NSLog(@"name: %@ date: %@", name, date);
    

    which finally yields:

    name: his name date: Mon Mar 18 16:16:43 2019
    

    I don't especially recommend this alternative, but it has its niceties and benefits.

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  • 2021-02-13 04:21

    You can use the STL in Objective-C++. All you need to do is change the extension of your .m file to .mm and I would also advise you use #import instead of #include. That way you can use your pair STL container.

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