Blocks in Objective-C

Function values with the famous inside-out type spelling.

#import <Foundation/Foundation.h>

// A typedef tames the block type's inside-out spelling.
typedef NSString *(^Labeler)(NSString *);

int main(void) {
    @autoreleasepool {
        // ^ opens a block literal: a function value with a body.
        Labeler tag = ^NSString *(NSString *title) {
            return [NSString stringWithFormat:@"[USED] %@", title];
        };
        NSLog(@"%@", tag(@"Court and Spark"));

        NSInteger (^discount)(NSInteger) = ^NSInteger(NSInteger cents) {
            return cents * 80 / 100;
        };
        NSLog(@"Sale price: %ld", (long)discount(2499));
    }
    return 0;
}

How it works

1. ^NSString *(NSString *title) { ... } is a block literal.
2. A typedef tames the declaration for reuse.
3. Blocks assign to variables and call like functions.

Keywords and builtins used here

• NSString
• int
• long
• main
• return
• typedef
• void

The run, in numbers

Lines

20

Characters to type

528

Tokens

111

Three-star pace

60 tpm

At the three-star pace of 60 tokens a minute, this run takes about 111 seconds.

Type this snippet

Step 1 of 3 in Blocks, step 16 of 27 in Language basics.

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Blocks in other languages

• Smalltalk