Objective-C Programming: The Big Nerd Ranch Guide

28 Blocks

A block is a chunk of code. Here is a block:

^{
    NSLog(@"This is an instruction within a block.");
}

It looks like a C function; it is a set of instructions inside curly braces. It does not, however, have a name. Instead, the caret (^) identifies this bit of code as a block.

Like a function, a block can take arguments and return values. Here is another block:

^(double dividend, double divisor) {
    double quotient = dividend / divisor;
    return quotient;
}

This block takes two doubles as arguments and returns a double.

You can pass a block as an argument to a method that accepts a block. Many of Apple’s classes have methods that accept blocks as arguments.

For instance, NSArray, NSDictionary, and NSSet allow block-based ...