Functions as types in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function type variable that takes two Ints and returns an Int.

Swift

var operation: [1]

Drag options to blanks, or click blank then click option'

Afunc(Int, Int) -> Int

BInt -> Int

CInt, Int -> Int

D(Int, Int) -> Int

Attempts:

3 left

💡 Hint

Common Mistakes

Writing function types without parentheses around input parameters.

Using 'func' keyword inside the type declaration.

In Swift, a function type is written as (InputTypes) -> ReturnType. Here, the function takes two Ints and returns an Int, so the correct type is (Int, Int) -> Int.

2fill in blank

medium

Complete the code to assign a function that adds two Ints to the variable 'operation'.

Swift

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

var operation: (Int, Int) -> Int = [1]

Drag options to blanks, or click blank then click option'

Aadd(a:b:)

Badd

Cadd()

Dadd(a, b)

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the function with parentheses instead of referencing it.

Omitting parameter labels in the function reference.

In Swift, to assign a function to a variable, you use the function's name with its parameter labels and colon, like 'add(a:b:)'.

3fill in blank

hard

Fix the error in the function type declaration that should accept a String and return a Bool.

Swift

var check: [1]

Drag options to blanks, or click blank then click option'

AString -> Bool

B(String) -> Bool

C(String, Bool)

Dfunc(String) -> Bool

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses around input types.

Including 'func' keyword in the type.

The correct function type syntax uses parentheses around input types and an arrow to the return type, like (String) -> Bool.

4fill in blank

hard

Fill both blanks to create a dictionary that maps String keys to functions taking Int and returning String.

Swift

var handlers: [[1]: [2]] = [:]

Drag options to blanks, or click blank then click option'

AString

B(Int) -> String

CInt

DString -> Int

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping key and value types.

Using incorrect function type syntax.

The dictionary keys are Strings, and the values are functions with type (Int) -> String.

5fill in blank

hard

Fill all three blanks to define a function that takes a function as parameter and returns an Int.

Swift

func performOperation(_ op: [1]) -> [2] {
    return op(5, 3)
}

let add: [3] = { $0 + $1 }

Drag options to blanks, or click blank then click option'

A(Int, Int) -> Int

BInt

D()->Void

Attempts:

3 left

💡 Hint

Common Mistakes

Using inconsistent types for function parameter and closure.

Wrong return type for performOperation.

The function parameter 'op' is a function type (Int, Int) -> Int, the return type is Int, and 'add' is a closure of type (Int, Int) -> Int.

Practice

1. What does it mean when we say "functions are types" in Swift?

easy

A. Functions can be stored in variables and passed around like values.

B. Functions cannot be assigned to variables.

C. Functions must always return an Int type.

D. Functions cannot accept parameters.

Solution

1. Step 1: Understand the concept of types in Swift

   In Swift, types define what kind of values variables can hold.

2. Step 2: Apply this to functions

   Functions have types too, meaning they can be assigned to variables, passed as arguments, or returned from other functions.

3. Final Answer:

   Functions can be stored in variables and passed around like values. -> Option A

4. Quick Check:

   Functions as values = Functions can be stored in variables and passed around like values. [OK]

Hint: Remember: functions behave like any other value in Swift [OK]

Common Mistakes:

• Thinking functions can't be assigned to variables
• Assuming functions must return Int
• Believing functions can't take parameters

2. Which of the following is the correct way to declare a variable that holds a function taking two Ints and returning an Int?

easy

A. var operation: (Int, Int) Int

B. var operation: Int -> Int -> Int

C. var operation: (Int Int) -> Int

D. var operation: (Int, Int) -> Int

Solution

1. Step 1: Recall Swift function type syntax

   Function types are written as (ParameterTypes) -> ReturnType, with parameters separated by commas.

2. Step 2: Check each option

   var operation: (Int, Int) -> Int correctly uses (Int, Int) -> Int. Others have syntax errors or missing arrows.

3. Final Answer:

   var operation: (Int, Int) -> Int -> Option D

4. Quick Check:

   Correct function type syntax = var operation: (Int, Int) -> Int [OK]

Hint: Use (Type1, Type2) -> ReturnType for function types [OK]

Common Mistakes:

• Omitting commas between parameter types
• Missing arrow '->' in function type
• Incorrect parameter grouping

3. What will be the output of the following Swift code?

func add(_ a: Int, _ b: Int) -> Int { a + b }
var mathOperation: (Int, Int) -> Int = add
print(mathOperation(3, 4))

medium

A. 7

B. 34

C. Error: Cannot assign function

D. 0

Solution

1. Step 1: Understand function assignment

   The function 'add' matches the type (Int, Int) -> Int, so it can be assigned to 'mathOperation'.

2. Step 2: Evaluate the function call

   Calling mathOperation(3, 4) calls add(3, 4), which returns 3 + 4 = 7.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   Function call result = 7 [OK]

Hint: Assign matching function types to variables to call them [OK]

Common Mistakes:

• Expecting string concatenation instead of addition
• Thinking function assignment causes error
• Confusing function call syntax

4. Identify the error in this Swift code snippet:

var multiply: (Int, Int) -> Int
multiply = { a, b in a * b }
print(multiply(2))

medium

A. Missing return statement in closure

B. Variable multiply not initialized

C. Calling multiply with wrong number of arguments

D. Incorrect closure syntax

Solution

1. Step 1: Check closure assignment

   The closure { a, b in a * b } correctly matches (Int, Int) -> Int type.

2. Step 2: Check function call

   Calling multiply(2) provides only one argument, but multiply expects two Ints.

3. Final Answer:

   Calling multiply with wrong number of arguments -> Option C

4. Quick Check:

   Argument count mismatch = Calling multiply with wrong number of arguments [OK]

Hint: Match argument count with function type parameters [OK]

Common Mistakes:

• Assuming closure needs explicit return
• Ignoring argument count in function call
• Thinking variable is uninitialized

5. Given the function type (Int) -> (Int) -> Int, what does this type represent in Swift?

hard

A. A function that takes an Int and returns an Int array.

B. A function that takes an Int and returns another function that takes an Int and returns an Int.

C. A function that takes two Ints and returns an Int.

D. A function that takes no parameters and returns an Int.

Solution

1. Step 1: Analyze the nested function type

   The type (Int) -> (Int) -> Int means the function takes one Int and returns another function.

2. Step 2: Understand the returned function

   The returned function itself takes an Int and returns an Int.

3. Final Answer:

   A function that takes an Int and returns another function that takes an Int and returns an Int. -> Option B

4. Quick Check:

   Curried function type = A function that takes an Int and returns another function that takes an Int and returns an Int. [OK]

Hint: Read from left to right: input then output, output can be a function [OK]

Common Mistakes:

• Confusing nested function types with multiple parameters
• Assuming it returns an array
• Ignoring that return type can be a function