Star projection for unknown types in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a list with star projection.

Kotlin

val list: List<[1]> = listOf("apple", "banana", "cherry")

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

A*

Bout Any

CAny

D?

Attempts:

3 left

💡 Hint

Common Mistakes

Using '?' instead of '*' for star projection.

Using 'Any' which is a specific type, not a star projection.

The star projection is represented by '*' in Kotlin generics to indicate an unknown type.

2fill in blank

medium

Complete the function parameter type using star projection.

Kotlin

fun printList(list: List<[1]>) {
    for (item in list) {
        println(item)
    }
}

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

A*

BAny

Cout Any

Din Any

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Any' which restricts the type to Any only.

Using 'out Any' or 'in Any' which are variance annotations, not star projections.

Using '*' as star projection allows the function to accept a list of any type.

3fill in blank

hard

Fix the error in the generic function using star projection.

Kotlin

fun <T> copy(from: Array<out [1]>, to: Array<[1]>) {
    for (i in from.indices) {
        to[i] = from[i]
    }
}

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

AAny

Bout Any

CT

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' inside function generic parameters which is invalid.

Using 'Any' which loses type safety.

The generic type parameter 'T' should be used consistently instead of star projection in this function.

4fill in blank

hard

Fill both blanks to create a map with star projections for keys and values.

Kotlin

val map: Map<[1], [2]> = mapOf("one" to 1, "two" to 2)

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

A*

BAny

Cout Any

Din Any

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Any' which is a specific type, not star projection.

Mixing variance annotations like 'out Any' or 'in Any' incorrectly.

Star projection '*' is used for both key and value types to indicate unknown types.

5fill in blank

hard

Fill all three blanks to declare a function with star projections and variance.

Kotlin

fun process(list: List<[1]>, producer: Producer<[2]>, consumer: Consumer<[3]>) {
    // function body
}

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

A*

Bout Any

Cin Any

DAny

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Any' instead of variance annotations for producer and consumer.

Using star projection in variance positions incorrectly.

Star projection '*' is used for the list, 'out Any' for producer (covariant), and 'in Any' for consumer (contravariant).