Mutable collections in Objective-C

The mutable classes subclass the immutable ones and add writers.

#import <Foundation/Foundation.h>

int main(void) {
    @autoreleasepool {
        // Mutable classes subclass the immutable ones and add writers.
        NSMutableArray<NSString *> *wants =
            [@[ @"Blue Train", @"Nefertiti" ] mutableCopy];
        [wants addObject:@"Speak No Evil"];
        [wants removeObject:@"Nefertiti"];
        NSLog(@"Want list: %@", [wants componentsJoinedByString:@", "]);

        NSMutableDictionary<NSString *, NSNumber *> *prices =
            [[NSMutableDictionary alloc] init];
        prices[@"Blue Train"] = @29;
        prices[@"Speak No Evil"] = @24;
        [prices removeObjectForKey:@"Blue Train"];
        NSLog(@"Priced titles: %lu", (unsigned long)[prices count]);
    }
    return 0;
}

How it works

1. mutableCopy turns a literal into something editable.
2. addObject: and removeObject: reshape the array.
3. Subscript assignment writes into a mutable dictionary.

Keywords and builtins used here

• NSMutableArray
• NSMutableDictionary
• NSNumber
• NSString
• int
• long
• main
• return
• unsigned
• void

The run, in numbers

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20

Characters to type

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Tokens

135

Three-star pace

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Type this snippet

Step 3 of 3 in Collections, step 12 of 27 in Language basics.

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