Closures and Higher-Order Functions

Closures and Higher-Order Functions

In this lesson — part of Advanced Features — you'll learn closures and higher-order functions in Swift and why it matters in real work.

Why it matters

Functions that take or return functions unlock concise, composable code.

Key ideas

• Functions as values
• map / filter / reduce
• Callbacks
• Composition

In practice

Here's how it looks in idiomatic Swift:

let nums = [1, 2, 3, 4, 5, 6]
let evensDoubled = nums
    .filter { $0 % 2 == 0 }
    .map { $0 * 2 }
print(evensDoubled)   // [4, 8, 12]

Swift note: Swift's map/filter take closures where $0 is the shorthand for the first argument, and trailing-closure syntax lets you drop the parentheses.

Try it yourself

Exercise: In Swift, use map and filter to get the squares of the even numbers.

Recap

You now understand closures and higher-order functions and can apply it in Swift. Mark this lesson complete and continue to the next one.