Custom delegated properties in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a delegated property using the 'by' keyword.

Kotlin

val myValue: String [1] MyDelegate()

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

Aby

Bwith

Cusing

Dfrom

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'with' or 'from' instead of 'by' causes syntax errors.

Forgetting the keyword entirely.

In Kotlin, delegated properties use the 'by' keyword to delegate the property implementation to another object.

2fill in blank

medium

Complete the operator function to get the value of the delegated property.

Kotlin

operator fun getValue(thisRef: Any?, property: KProperty<*>): String [1] "Hello from delegate"

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Ayield

Bprint

Creturn

Dthrow

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'print' instead of 'return' does not provide the value.

Using 'throw' causes an exception.

The 'getValue' operator function must return the value of the property, so it uses 'return'.

3fill in blank

hard

Fix the error in the setValue operator function to correctly assign the new value.

Kotlin

operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
    [1] = value
}

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Aproperty

BstoredValue

Cfield

DthisRef

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to assign to 'property' or 'thisRef' causes errors.

Using 'field' outside of property setter is invalid.

The delegate must assign the new value to its own storage variable, here named 'storedValue'.

4fill in blank

hard

Fill both blanks to create a delegate that stores and returns an integer value.

Kotlin

class IntDelegate {
    private var [1] = 0
    operator fun getValue(thisRef: Any?, property: KProperty<*>): Int = [2]
}

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AstoredValue

Bvalue

Dproperty

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' in getValue is incorrect because it's not defined there.

Using 'property' as a value causes errors.

The delegate uses 'storedValue' to keep the integer and returns it in getValue.

5fill in blank

hard

Fill all three blanks to complete a delegate that logs and stores a string property.

Kotlin

class LoggingDelegate {
    private var [1] = ""
    operator fun getValue(thisRef: Any?, property: KProperty<*>): String {
        println("Getting value of ${property.name}")
        return [2]
    }
    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {
        println("Setting value of ${property.name} to $value")
        [3] = value
    }
}

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

AstoredValue

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'value' as a variable name for storage causes confusion.

Forgetting to return the stored value in getValue.

The delegate uses 'storedValue' to keep the string, returns it in getValue, and assigns it in setValue.