It keyword for single parameter in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the it keyword represent in Kotlin lambdas with a single parameter?

In Kotlin, it is an implicit name for the single parameter in a lambda expression when the parameter name is not explicitly specified.

beginner

How do you use it in a Kotlin lambda to print each element of a list?

You can write list.forEach { println(it) }. Here, it refers to each element of the list during iteration.

intermediate

Can you use it if your lambda has more than one parameter?

No. The it keyword is only available when the lambda has exactly one parameter. For multiple parameters, you must name them explicitly.

beginner

Rewrite this lambda using it: list.map { number -> number * 2 }

Using it, it becomes list.map { it * 2 }. This works because the lambda has a single parameter.

beginner

Why is using it helpful in Kotlin lambdas?

Using it makes the code shorter and cleaner when the lambda has only one parameter, improving readability.

In Kotlin, when can you use the it keyword inside a lambda?

A When the lambda has no parameters

B When the lambda has exactly one parameter

C When the lambda has multiple parameters

D Only in functions, not lambdas

it is the implicit name for the single parameter in a lambda with exactly one parameter.

What does it represent in this code: list.forEach { println(it) }?

A The current element of the list

B The index of the element

C The entire list

D A Boolean value

it refers to each element of the list as the lambda runs for each item.

Which of these is a correct use of it in Kotlin?

A list.map { it * 2 }

B list.map { a, b -> it + b }

C list.filter { }

D list.forEach { println() }

it can only be used when the lambda has one parameter, like in list.map { it * 2 }.

If a lambda has two parameters, how do you refer to them?

A Use <code>it</code> for the first and <code>that</code> for the second

B You cannot use lambdas with two parameters

C Use <code>it</code> for both

D You must name both parameters explicitly

When there are multiple parameters, you must name them explicitly in the lambda.

What is the benefit of using it in Kotlin lambdas?

A Improves performance

B Allows lambdas to have multiple parameters

C Makes code shorter and easier to read for single-parameter lambdas

D Automatically types the parameter

it helps keep code concise and clean when the lambda has one parameter.

Explain how the it keyword works in Kotlin lambdas and when you can use it.

Think about how Kotlin lets you skip naming the parameter when there is only one.

Give an example of a Kotlin lambda using it and explain what it refers to in your example.

Try a simple list operation like forEach or map.

Practice

1. What does the it keyword represent in a Kotlin lambda with a single parameter?

easy

A. The single implicit parameter of the lambda

B. A reserved word for loop counters

C. A keyword to declare variables

D. A function to print output

Solution

1. Step 1: Understand lambda parameters

   In Kotlin, if a lambda has only one parameter, you don't need to name it explicitly.

2. Step 2: Role of it

   The keyword it automatically refers to that single parameter inside the lambda.

3. Final Answer:

   The single implicit parameter of the lambda -> Option A

4. Quick Check:

   it = single lambda parameter [OK]

Hint: Remember: it means the one lambda input [OK]

Common Mistakes:

• Thinking it is a loop variable
• Confusing it with a keyword to declare variables
• Assuming it prints output

2. Which of the following is the correct syntax to use it in a Kotlin lambda that doubles each number in a list?

easy

A. list.map { it * 2 }

B. list.map { x -> x * 2 }

C. list.map { it -> it * 2 }

D. list.map { * 2 }

Solution

1. Step 1: Identify lambda with single parameter

   The lambda inside map has one parameter, so it can be used implicitly.

2. Step 2: Check syntax correctness

   list.map { it * 2 } correctly uses it without naming the parameter explicitly.

3. Final Answer:

   list.map { it * 2 } -> Option A

4. Quick Check:

   Implicit single parameter lambda syntax = list.map { it * 2 } [OK]

Hint: Use it only when lambda has one parameter [OK]

Common Mistakes:

• Using explicit parameter name and it together
• Omitting parameter name but adding arrow
• Trying to multiply without parameter

3. What is the output of this Kotlin code?

val numbers = listOf(1, 2, 3)
val result = numbers.filter { it > 1 }
println(result)

medium

A. [1, 2, 3]

B. [1]

C. [2, 3]

D. []

Solution

1. Step 1: Understand the filter condition

   The lambda filters numbers where it > 1, so only numbers greater than 1 remain.

2. Step 2: Apply filter to the list

   From the list [1, 2, 3], numbers 2 and 3 satisfy the condition.

3. Final Answer:

   [2, 3] -> Option C

4. Quick Check:

   Filter with it > 1 = [2, 3] [OK]

Hint: Filter keeps items where it meets condition [OK]

Common Mistakes:

• Including 1 in the result
• Confusing filter with map
• Expecting original list unchanged

4. Identify the error in this Kotlin code snippet:

val list = listOf(1, 2, 3)
val doubled = list.map { it * }
println(doubled)

medium

A. Missing parameter name before *

B. No error, code runs fine

C. Using it without declaring lambda parameter

D. Syntax error: incomplete expression after *

Solution

1. Step 1: Analyze the lambda expression

   The expression it * is incomplete; it lacks a value after the multiplication operator.

2. Step 2: Identify syntax error

   This causes a syntax error because Kotlin expects a complete expression after *.

3. Final Answer:

   Syntax error: incomplete expression after * -> Option D

4. Quick Check:

   Incomplete expression causes syntax error [OK]

Hint: Check for complete expressions after operators [OK]

Common Mistakes:

• Assuming it * is valid alone
• Thinking it must be declared explicitly
• Ignoring syntax errors

5. Given a list of strings val words = listOf("apple", "banana", "cat"), which Kotlin code uses it correctly to create a list of word lengths greater than 3?

hard

A. words.map { it.length > 3 }

B. words.filter { it.length > 3 }

C. words.map { it.length }.filter { it > 3 }

D. words.filter { length > 3 }.map { it }

Solution

1. Step 1: Understand the goal

   We want words whose lengths are greater than 3, so we filter words based on their length.

2. Step 2: Analyze each option

   words.filter { it.length > 3 }, words.filter { it.length > 3 }, correctly filters the words list to include only words with length greater than 3, using it properly.

3. Final Answer:

   words.filter { it.length > 3 } -> Option B

4. Quick Check:

   Filter words by length > 3 = words.filter { it.length > 3 } [OK]

Hint: Use filter with it.length > 3 to get words longer than 3 [OK]

Common Mistakes:

• Filtering on string directly without length
• Using it incorrectly in filter
• Mixing order of map and filter