Functions as types in Swift - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Swift code using function types?

Consider the following Swift code. What will it print when run?

Swift

func add(_ a: Int, _ b: Int) -> Int {
    return a + b
}

let operation: (Int, Int) -> Int = add
print(operation(3, 4))

A 7

B 34

C Error: Cannot assign function to variable

D 0

💡 Hint

Remember that the variable 'operation' holds a function that adds two numbers.

The variable 'operation' is assigned the function 'add' which sums two integers. Calling operation(3, 4) returns 7.

🧠 Conceptual

intermediate

What is the type of this Swift function variable?

Given the declaration: let transform: (String) -> Int, what does this type mean?

A A function that takes a String and returns an Int

B A function that takes an Int and returns a String

C A variable holding a String value

D A function that takes no parameters and returns nothing

💡 Hint

Look at the arrow (->) in the type declaration.

The type (String) -> Int means a function that accepts a String input and returns an Int output.

🔧 Debug

advanced

Why does this Swift code cause a compile error?

Examine the code below and choose the reason it fails to compile.

Swift

func multiply(_ x: Int, _ y: Int) -> Int {
    return x * y
}

let operation: (Int) -> Int = multiply
print(operation(5))

A Missing return statement in 'multiply' function

B Type mismatch: 'multiply' expects two Ints but 'operation' expects one Int

C Cannot assign a function to a constant

D Function 'multiply' is not defined

💡 Hint

Check the number of parameters expected by the function and the variable.

The variable 'operation' expects a function taking one Int, but 'multiply' requires two Ints, causing a type mismatch.

🚀 Application

advanced

Which option correctly uses a function type as a parameter?

You want to write a Swift function 'applyTwice' that takes a function from Int to Int and an Int, then applies the function twice. Which code correctly defines 'applyTwice'?

A

func applyTwice(_ f: (Int, Int) -> Int, _ x: Int) -> Int {
    return f(x, x)
}

B

func applyTwice(f: Int, x: Int) -> Int {
    return f + x
}

C

func applyTwice(_ f: (Int) -> Int, _ x: Int) -> Int {
    return f(f(x))
}

D

func applyTwice(_ f: Int, _ x: Int) -> Int {
    return f * x
}

💡 Hint

The parameter 'f' should be a function that takes one Int and returns an Int.

Option C correctly defines 'applyTwice' taking a function (Int) -> Int and applies it twice to 'x'. Other options have wrong parameter types or logic.

❓ Predict Output

expert

What is the output of this Swift code using nested function types?

Analyze the code and select the output it produces.

Swift

func makeAdder(_ x: Int) -> (Int) -> Int {
    func adder(_ y: Int) -> Int {
        return x + y
    }
    return adder
}

let addFive = makeAdder(5)
print(addFive(10))

A Error: Cannot return nested function

B 510

C 5

D 15

💡 Hint

The function 'makeAdder' returns a function that adds 'x' to its input.

The function 'makeAdder' returns 'adder' which adds 'x' (5) to its argument (10), so output is 15.