Sorting with comparators in Objective-C

A block returns ascending, same, or descending; the array obeys.

#import <Foundation/Foundation.h>

int main(void) {
    @autoreleasepool {
        NSArray<NSNumber *> *years = @[ @1971, @1959, @1977, @1965 ];

        // A comparator block returns ascending, same, or descending.
        NSArray<NSNumber *> *sorted =
            [years sortedArrayUsingComparator:
                ^NSComparisonResult(NSNumber *a, NSNumber *b) {
                    return [a compare:b];
                }];
        NSLog(@"Oldest press: %@", [sorted firstObject]);
        NSLog(@"In order: %@", [sorted componentsJoinedByString:@", "]);
    }
    return 0;
}

How it works

1. sortedArrayUsingComparator: returns a new sorted array.
2. [a compare:b] already speaks NSComparisonResult.
3. The original array is untouched — immutable in, immutable out.

Keywords and builtins used here

• NSArray
• NSNumber
• int
• main
• return
• void

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Step 3 of 3 in Enumeration, step 15 of 27 in Language basics.

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