Vararg parameters in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does vararg mean in Kotlin function parameters?

vararg allows a function to accept zero or more arguments of the specified type as a single parameter.

It lets you pass multiple values without creating an array explicitly.

beginner

How do you call a Kotlin function that has a vararg parameter?

You can pass multiple arguments separated by commas, or pass an array using the spread operator *.

Example: fun printAll(vararg strings: String) can be called as printAll("a", "b", "c") or printAll(*arrayOf("a", "b")).

intermediate

Can a Kotlin function have more than one vararg parameter?

No, a function can have only one vararg parameter.

If there are other parameters, they must come before or after the vararg parameter, but only one can be vararg.

beginner

What type does a vararg parameter have inside the function?

Inside the function, the vararg parameter is seen as an array of the specified type.

For example, vararg numbers: Int is treated as IntArray inside the function.

beginner

Why use vararg instead of an array parameter?

vararg makes calling the function easier and cleaner because you can pass multiple arguments directly without creating an array.

It improves readability and convenience.

What keyword is used in Kotlin to allow a function to accept multiple arguments as one parameter?

A multiple

B spread

C vararg

D params

vararg is the correct keyword to accept multiple arguments in Kotlin.

How do you pass an existing array to a vararg parameter?

A Just pass the array directly

B Convert the array to a list first

C You cannot pass an array to a vararg parameter

D Use the spread operator <code>*</code> before the array

You use the spread operator * to pass an array to a vararg parameter.

Inside the function, a vararg parameter is treated as:

A An array

B A single value

C A map

D A list

Inside the function, a vararg parameter is an array of the specified type.

Can a Kotlin function have two vararg parameters?

A No, only one <code>vararg</code> parameter is allowed

B Yes, always

C Yes, but only if they have different types

D Only if they are at the end of the parameter list

Kotlin allows only one vararg parameter per function.

Which of these is a benefit of using vararg parameters?

A You must always create an array before calling the function

B It makes function calls cleaner by allowing multiple arguments directly

C It restricts the number of arguments to one

D It automatically converts arguments to strings

vararg lets you pass multiple arguments directly, making calls cleaner and easier.

Explain what vararg parameters are and how you use them in Kotlin functions.

Think about how you can pass many values to one parameter.

Describe the rules and limitations when using vararg parameters in Kotlin functions.

Consider how many varargs you can have and where they appear.

Practice

1.

What does the vararg keyword do in Kotlin functions?

easy

A. Allows passing a variable number of arguments to a function

B. Declares a function that returns multiple values

C. Defines a function with no parameters

D. Specifies a function that accepts only one argument

Solution

1. Step 1: Understand the purpose of vararg

   The vararg keyword lets a function accept zero or more arguments of the same type without needing an array or list explicitly.

2. Step 2: Compare options with this meaning

   Only Allows passing a variable number of arguments to a function correctly describes this behavior, while others describe unrelated function features.

3. Final Answer:

   Allows passing a variable number of arguments to a function -> Option A

4. Quick Check:

   Vararg = variable arguments [OK]

Hint: Vararg means many arguments, not just one [OK]

Common Mistakes:

• Thinking vararg returns multiple values
• Confusing vararg with no parameters
• Assuming vararg limits to one argument

2.

Which of the following is the correct syntax to declare a function with a vararg parameter in Kotlin?

fun printAll(____ numbers: Int) { for (n in numbers) println(n) }

easy

A. var

B. varargs

C. vararg

D. args

Solution

1. Step 1: Recall the exact keyword for variable arguments

   Kotlin uses vararg (singular) to declare variable number of arguments.

2. Step 2: Check each option

   Only vararg matches the correct keyword; others are incorrect or invalid syntax.

3. Final Answer:

   vararg -> Option C

4. Quick Check:

   Keyword is vararg, not varargs [OK]

Hint: Remember: vararg is singular keyword [OK]

Common Mistakes:

• Using 'varargs' instead of 'vararg'
• Omitting the keyword entirely
• Using 'var' or 'args' which are invalid here

3.

What is the output of this Kotlin code?

fun sumAll(vararg numbers: Int): Int { var sum = 0; for (n in numbers) sum += n; return sum }

fun main() {
  println(sumAll(1, 2, 3))
  println(sumAll())
}

medium

A. Error and error

B. 6 and error

C. Error and 0

D. 6 and 0

Solution

1. Step 1: Understand the function behavior with vararg

   The function sums all integers passed. If no arguments, the loop does not run, sum stays 0.

2. Step 2: Calculate outputs for calls

   sumAll(1,2,3) = 1+2+3 = 6; sumAll() = 0 (no arguments)

3. Final Answer:

   6 and 0 -> Option D

4. Quick Check:

   Sum of inputs or zero if none [OK]

Hint: Vararg can be empty, sum then zero [OK]

Common Mistakes:

• Assuming empty vararg causes error
• Forgetting sum starts at zero
• Confusing vararg with list requiring explicit array

4.

Identify the error in this Kotlin function declaration:

fun printNames(vararg names: String, age: Int) {
  for (name in names) println(name)
  println(age)
}

medium

A. Function cannot have more than one parameter

B. Vararg parameter must be the last parameter

C. Vararg parameter cannot be of type String

D. Vararg parameters must be declared with 'varargs'

Solution

1. Step 1: Recall vararg parameter position rule

   Kotlin requires the vararg parameter to be the last in the parameter list.

2. Step 2: Check the function parameters

   Here, vararg names is before age, which is invalid syntax.

3. Final Answer:

   Vararg parameter must be the last parameter -> Option B

4. Quick Check:

   Vararg last parameter rule [OK]

Hint: Vararg must always be last parameter [OK]

Common Mistakes:

• Placing vararg parameter before others
• Thinking vararg can be anywhere
• Using 'varargs' instead of 'vararg'

5.

Given this function:

fun combine(vararg parts: String): String {
  return parts.joinToString(separator = ", ")
}

Which call correctly passes an existing array val arr = arrayOf("a", "b", "c") to combine?

hard

A. combine(*arr)

B. combine(arr)

C. combine(arr.toList())

D. combine(arr as String)

Solution

1. Step 1: Understand how to pass an array to vararg

   Kotlin requires the spread operator * to pass an array as vararg arguments.

2. Step 2: Evaluate each option

   combine(*arr) uses *arr, correctly spreading the array. combine(arr) passes the array as a single argument, not vararg. combine(arr.toList()) passes a list, not vararg. combine(arr as String) is invalid cast.

3. Final Answer:

   combine(*arr) -> Option A

4. Quick Check:

   Use * to spread array for vararg [OK]

Hint: Use * to spread array into vararg [OK]

Common Mistakes:

• Passing array without * operator
• Passing list instead of array
• Trying invalid casts to String