Destructuring in collection iteration in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to destructure each pair in the list and print the key.

Kotlin

val pairs = listOf("a" to 1, "b" to 2)
for (([1], value) in pairs) {
    println([1])
}

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

Akey

Bfirst

Citem

Delement

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'key' or 'item' which are not the default names for Pair components.

In Kotlin, when destructuring a Pair, the first element is commonly named 'first'.

2fill in blank

medium

Complete the code to destructure map entries and print both key and value.

Kotlin

val map = mapOf("x" to 10, "y" to 20)
for (([1], value) in map) {
    println("Key: $[1], Value: $value")
}

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

Aentry

Belement

Cindex

Dkey

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'entry' or 'index' which are not valid destructuring names for map entries.

When iterating over a map, destructuring uses 'key' and 'value' to access entries.

3fill in blank

hard

Fix the error in destructuring a list of triples to print all three elements.

Kotlin

val triples = listOf(Triple(1, "a", true), Triple(2, "b", false))
for ((first, [1], third) in triples) {
    println("$first, $[1], $third")
}

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

Asecond

Bmiddle

Cvalue

Ditem

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'middle' or 'value' which are not valid component names for Triple.

Triple destructuring uses 'first', 'second', and 'third' as component names.

4fill in blank

hard

Fill both blanks to destructure a list of pairs and print their sum.

Kotlin

val pairs = listOf(1 to 2, 3 to 4)
for (([1], [2]) in pairs) {
    println([1] + [2])
}

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

Afirst

Bsecond

Ckey

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'key' and 'value' which are for map entries, not pairs.

Pairs are destructured into 'first' and 'second' components in Kotlin.

5fill in blank

hard

Fill all three blanks to destructure a list of triples and print a formatted string.

Kotlin

val triples = listOf(Triple("John", "Doe", 30), Triple("Jane", "Smith", 25))
for (([1], [2], [3]) in triples) {
    println("Name: $[1] $[2], Age: $[3]")
}

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

Afirst

Blast

Cthird

Dsecond

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'last' instead of 'second' for the middle element.

Triple destructuring uses 'first', 'second', and 'third' to access elements in order.

Practice

1. What does destructuring in Kotlin collection iteration allow you to do?
for ((key, value) in map) { ... }

easy

A. Only access the value in the loop

B. Only access the key in the loop

C. Access both key and value directly in the loop variables

D. Modify the map while iterating

Solution

1. Step 1: Understand destructuring syntax

   In Kotlin, for ((key, value) in map) extracts both key and value from each map entry.

2. Step 2: Recognize loop variable usage

   This lets you use key and value directly inside the loop without extra calls.

3. Final Answer:

   Access both key and value directly in the loop variables -> Option C

4. Quick Check:

   Destructuring = direct access to parts [OK]

Hint: Destructuring splits pairs into variables directly [OK]

Common Mistakes:

• Thinking only key or value is accessible
• Trying to modify map inside loop
• Not using parentheses for destructuring

2. Which of the following is the correct syntax for destructuring a map in Kotlin?
val map = mapOf("a" to 1, "b" to 2)

easy

A. for (key, value in map) { println(key + value) }

B. for ((key, value) in map) { println(key + value) }

C. for [key, value] in map { println(key + value) }

D. for {key, value} in map { println(key + value) }

Solution

1. Step 1: Recall Kotlin destructuring syntax

   Kotlin requires parentheses around variables when destructuring: for ((key, value) in map).

2. Step 2: Check each option

   Only for ((key, value) in map) { println(key + value) } uses parentheses correctly; others use commas without parentheses or wrong brackets.

3. Final Answer:

   for ((key, value) in map) { println(key + value) } -> Option B

4. Quick Check:

   Parentheses needed for destructuring [OK]

Hint: Use parentheses around variables in destructuring [OK]

Common Mistakes:

• Omitting parentheses in for loop
• Using square or curly brackets instead
• Confusing destructuring with tuple unpacking syntax

3. What is the output of this Kotlin code?

val map = mapOf("x" to 10, "y" to 20)
for ((k, v) in map) {
  println("$k$v")
}

medium

A. Syntax error

B. 10x\n20y

C. k v\nk v

D. x10\ny20

Solution

1. Step 1: Understand map entries and destructuring

   The map has entries "x" to 10 and "y" to 20. The loop destructures each entry into k and v.

2. Step 2: Print key and value concatenated

   Inside the loop, println("$k$v") prints key and value together without space, so outputs are "x10" and "y20" on separate lines.

3. Final Answer:

   x10\ny20 -> Option D

4. Quick Check:

   Print key + value per entry [OK]

Hint: Destructure map entries to print key and value [OK]

Common Mistakes:

• Swapping key and value in output
• Expecting spaces between key and value
• Confusing variable names

4. Identify the error in this Kotlin code snippet:

val map = mapOf("a" to 1, "b" to 2)
for (key, value in map) {
  println(key + value)
}

medium

A. Missing parentheses around key and value in for loop

B. mapOf cannot be iterated

C. Cannot add key and value directly

D. No error, code runs fine

Solution

1. Step 1: Check for destructuring syntax

   The for loop uses for (key, value in map) which lacks parentheses around key, value.

2. Step 2: Understand correct syntax

   Kotlin requires parentheses for destructuring pairs: for ((key, value) in map). Without them, it's a syntax error.

3. Final Answer:

   Missing parentheses around key and value in for loop -> Option A

4. Quick Check:

   Parentheses required for destructuring [OK]

Hint: Always use parentheses for destructuring in for loops [OK]

Common Mistakes:

• Omitting parentheses in destructuring
• Thinking mapOf is not iterable
• Confusing addition with string concatenation

5. Given a list of pairs representing database rows:

val rows = listOf(Pair("id", 1), Pair("name", "Alice"), Pair("age", 30))

Which Kotlin code correctly prints each key and value using destructuring?

hard

A. for ((key, value) in rows) { println("$key: $value") }

B. for (key, value in rows) { println("$key: $value") }

C. for (row in rows) { println(row.key + ": " + row.value) }

D. for ((k, v) in rows) { println(k + v) }

Solution

1. Step 1: Recognize list of pairs and destructuring

   The list contains pairs, so destructuring with (key, value) works to access each part.

2. Step 2: Check each option for correctness

   for ((key, value) in rows) { println("$key: $value") } uses correct destructuring syntax and prints key and value with colon and space. for (key, value in rows) { println("$key: $value") } misses parentheses, for (row in rows) { println(row.key + ": " + row.value) } tries to access properties that don't exist, for ((k, v) in rows) { println(k + v) } concatenates without separator.

3. Final Answer:

   for ((key, value) in rows) { println("$key: $value") } -> Option A

4. Quick Check:

   Use parentheses and print with separator [OK]

Hint: Use parentheses and print key: value format [OK]

Common Mistakes:

• Omitting parentheses in for loop
• Accessing pair elements as properties
• Concatenating without separator