One of the key concepts of functional programming is that of a “higher-order function”. According
to Wikipedia, a higher-order function is a function that satisfies these two conditions:
• It takes one or more functions as input.
• It outputs a function.
In Objective-C, we often use blocks as functions.
We don’t have to look very far to find some higher-order functions baked into Foundation for us by
Apple. Consider a simple array of numbers:
1 NSArray *array = @[@(1), @(2), @(3)];
We might want to enumerate over the contents of that array, doing something with each element.
“Fine”, you say, “I’ll just write a for loop.”
Stop right there, buddy. As I’ve written before, stop writing for loops. There is a higher-order
function of NSArray’s that we can use, instead.
This code:
1 for (NSNumber *number in array) {
2 NSLog(@"%@", number);
3 }
… is equivalent to
