Closure expression syntax in Swift - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a closure expression in Swift?

A closure expression is a short, unnamed block of code that can be passed around and used in your code. It can capture values from its surrounding context.

beginner

How do you write a simple closure expression that adds two numbers in Swift?

You can write it like this: <br>

{ (a: Int, b: Int) -> Int in<br>  return a + b<br>}

beginner

What does the 'in' keyword do in a closure expression?

The 'in' keyword separates the closure's parameters and return type from the body of the closure.

intermediate

How can you simplify a closure expression in Swift?

You can omit parameter types, return type, and even the 'return' keyword if the closure has a single expression. Swift can infer these automatically.

intermediate

What are shorthand argument names in closure expressions?

Shorthand argument names like $0, $1 let you refer to closure parameters without naming them explicitly, making the closure shorter and cleaner.

What keyword separates parameters from the body in a Swift closure expression?

A let

B in

C return

D func

The 'in' keyword separates the closure's parameters and return type from its body.

Which of these is a valid way to write a closure that adds two Ints in Swift?

A closure add(a: Int, b: Int) { return a + b }

B func add(a: Int, b: Int) { a + b }

C let add = (a, b) => a + b

D { (a: Int, b: Int) -> Int in return a + b }

Option D shows the correct closure expression syntax in Swift.

How can you refer to the first parameter in a closure without naming it?

A $0

B param1

C first

D arg1

Shorthand argument names like $0 refer to the first parameter in a closure.

What can Swift infer in a closure expression to simplify the syntax?

A Function names

B Variable names

C Parameter types and return type

D Class names

Swift can infer parameter types and return type in closure expressions, allowing you to omit them.

Which of the following is NOT true about closure expressions in Swift?

A They must always have explicit parameter types

B They can capture values from their surrounding context

C They can be assigned to variables

D They can be passed as arguments to functions

Closure expressions do NOT always need explicit parameter types; Swift can infer them.

Explain the basic syntax of a closure expression in Swift and the role of the 'in' keyword.

Think about how you separate inputs from the code inside.

Describe how you can simplify closure expressions using Swift's type inference and shorthand argument names.

Swift helps you write less code by guessing types and letting you skip names.