Why functions are first-class in Kotlin - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a function variable that adds two numbers.

Kotlin

val add: (Int, Int) -> Int = [1]

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A{ a, b -> a + b }

Bfun add(a: Int, b: Int): Int = a + b

Ca + b

Dlambda(a, b) { a + b }

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign a function declaration instead of a lambda.

Using incorrect syntax like 'lambda' keyword which doesn't exist in Kotlin.

In Kotlin, you can assign a lambda expression to a variable to create a function value. The syntax { a, b -> a + b } defines a function that takes two integers and returns their sum.

2fill in blank

medium

Complete the code to pass a function as a parameter.

Kotlin

fun operate(x: Int, y: Int, operation: (Int, Int) -> Int): Int {
    return [1](x, y)
}

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

Ay

Boperation

Cx

Doperate

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the function by its own name instead of the parameter.

Using variables x or y as if they were functions.

The parameter operation is a function that takes two integers and returns an integer. To use it, call operation(x, y).

3fill in blank

hard

Fix the error in the code to assign a function reference to a variable.

Kotlin

fun greet(name: String) = "Hello, $name"

val greeter: (String) -> String = [1]

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A::greet

Bgreet.name

Cgreet()

Dgreet{}

Attempts:

3 left

💡 Hint

Common Mistakes

Adding parentheses which calls the function instead of referencing it.

Using invalid syntax like greet.name or greet{}.

To assign a function reference in Kotlin, use ::greet without parentheses. Using ::greet assigns the function itself, not the result of calling it.

4fill in blank

hard

Fill both blanks to create a list of functions and call the first one.

Kotlin

val functions = listOf<(Int) -> Int>({ x -> x * 2 }, [1])

val result = functions[0]([2])
println(result)

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A{ x -> x + 3 }

B5

C10

D{ y -> y - 1 }

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a function call instead of a lambda as the second list element.

Using a function call or variable instead of an integer argument.

The list contains two functions. The second function is a lambda that adds 3. To call the first function with an argument, pass a number like 5.

5fill in blank

hard

Fill all three blanks to filter and map a list using functions.

Kotlin

val numbers = listOf(1, 2, 3, 4, 5)

val filtered = numbers.filter [1] 
val mapped = filtered.map [2] 

println(mapped) // Output: [3]

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A{ it > 2 }

B{ it * 10 }

C[30, 40, 50]

D{ it < 3 }

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong filter condition like less than 3.

Mapping with addition instead of multiplication.

Expecting wrong output list.

The filter keeps numbers greater than 2. The map multiplies each by 10. So the output is [30, 40, 50].