Type inference by the compiler in Swift - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a variable with type inferred as Int.

Swift

var number = [1]

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

A"42"

B3.14

C42

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around the number makes it a String, not Int.

Using a decimal number makes it a Double, not Int.

The compiler infers the type of number as Int because the value 42 is an integer literal.

2fill in blank

medium

Complete the code to declare a constant with type inferred as Double.

Swift

let pi = [1]

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

A3.14159

B3

C"3.14159"

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using an integer literal will infer Int, not Double.

Using quotes makes it a String, not Double.

The compiler infers pi as Double because 3.14159 is a floating-point literal.

3fill in blank

hard

Fix the error in the code by completing the assignment with correct type inference.

Swift

var isActive = [1]

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

A1

Btrue

C"true"

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes makes it a String, not Bool.

Using numbers like 1 or 0 does not infer Bool.

The variable isActive is inferred as Bool when assigned the Boolean literal true.

4fill in blank

hard

Fill both blanks to create a dictionary with type inferred by the compiler.

Swift

let ages = [[1]: [2]]

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

A"Alice"

B30

C"Bob"

Dtrue

Attempts:

3 left

💡 Hint

Common Mistakes

Using Boolean values as dictionary values causes type mismatch.

Using numbers as keys without quotes causes errors.

The dictionary ages has keys of type String (like "Alice") and values of type Int (like 30), inferred by the compiler.

5fill in blank

hard

Fill all three blanks to filter the dictionary using a trailing closure with type inference and a condition.

Swift

let filteredAges = ages.filter { [1], [2] in [2] [3] 25 }

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

Aname

Bage

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong parameter names for keys or values.

Using the less than symbol reverses the filter condition.

This filter creates a dictionary with only entries where the age is greater than 25. The compiler infers the types from ages.