Extensions vs member functions priority in Kotlin - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the member function instead of the extension function.

Kotlin

class Example {
    fun greet() = "Member"
}

fun Example.greet() = "Extension"

fun main() {
    val ex = Example()
    println(ex.[1]())
}

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

Agreeting

Bgreet

CextensionGreet

DcallGreet

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the extension function by using a different name.

Assuming extension functions override member functions.

Member functions have higher priority than extension functions with the same name, so calling 'greet()' calls the member function.

2fill in blank

medium

Complete the code to call the extension function explicitly.

Kotlin

class Example {
    fun greet() = "Member"
}

fun Example.greet() = "Extension"

fun main() {
    val ex = Example()
    println([1](ex))
}

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

Agreet

Bex.greet

Cex.Extension.greet

DExample.greet

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the member function instead of the extension function.

Using incorrect syntax to call the extension function.

To call the extension function explicitly when a member function with the same name exists, use the syntax 'Example.greet()' with the receiver object.

3fill in blank

hard

Fix the error in calling the extension function inside another extension function.

Kotlin

class Example {
    fun greet() = "Member"
}

fun Example.greet() = "Extension"

fun Example.callGreet() = [1](this)

fun main() {
    val ex = Example()
    println(ex.callGreet())
}

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

AExample.greet

Bgreet

Cthis.greet

DcallGreet

Attempts:

3 left

💡 Hint

Common Mistakes

Calling 'greet()' without qualification calls the member function.

Using 'this.greet()' calls the member function, not the extension.

Inside an extension function, to call another extension function when a member function with the same name exists, qualify it with the class name.

4fill in blank

hard

Fill both blanks to define an extension function and call the member function inside it.

Kotlin

class Example {
    fun greet() = "Member"
}

fun Example.[1]() = "Extension calls " + this.[2]()

fun main() {
    val ex = Example()
    println(ex.greet())
    println(ex.[1]())
}

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

AgreetExtension

Bgreet

DgreetMember

Attempts:

3 left

💡 Hint

Common Mistakes

Naming the extension function the same as the member function.

Not calling the member function correctly inside the extension.

The extension function is named 'greetExtension' and calls the member function 'greet()' using 'this.greet()'.

5fill in blank

hard

Fill all three blanks to define an extension function that calls another extension and the member function.

Kotlin

class Example {
    fun greet() = "Member"
}

fun Example.[1]() = "Extension1"
fun Example.[2]() = "Extension2 calls " + [3].greet()

fun main() {
    val ex = Example()
    println(ex.greet())
    println(ex.[1]())
    println(ex.[2]())
}

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

Agreet1

Bgreet2

Cthis

DExample

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same name for both extension functions.

Using 'Example' instead of 'this' to call the member function.

The first extension is 'greet1', the second is 'greet2' which calls the member function 'greet()' on 'this' receiver.