also Scope Function in Kotlin

Introduction

also Scope Function is a fundamental concept every Kotlin developer should understand. Scope functions (let, run, with, apply, also) execute a block in the context of an object, reducing nesting and improving readability.

Also performs side effects and returns original object. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• also performs side effects and returns original object.
• Inside block, object is referenced as it.
• Useful for logging during chained calls.

Syntax

obj.also { ... }

also Scope Function in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val numbers = mutableListOf(1, 2)
    numbers.also { println("Before add: $it") }
        .add(3)
    println("After add: $numbers")
}

Sample Output

Before add: [1, 2]
After add: [1, 2, 3]

When to use

Use scope functions to configure objects, safely unwrap nullables, or chain transformations in a readable pipeline.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val numbers = mutableListOf(1, 2) assigns or updates a value used later in the program.

3. The println("Before add: $it") statement writes a line to the console — this produces part of the sample output below.

4. The println("After add: $numbers") statement writes a line to the console — this produces part of the sample output below.

5. Also performs side effects and returns original object.

6. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Understand the core idea: also performs side effects and returns original object.
• Prefer readable names and small functions so examples map directly to real projects.
• Run and modify the example — change values and observe how the output changes.

Common Mistakes

• Skipping the example and only reading the definition — hands-on practice cements the concept.
• Copying syntax without understanding nullable vs non-nullable types or scope rules.
• Ignoring compiler warnings that often point to safer alternatives.

Key Points

• also performs side effects and returns original object.
• Inside block, object is referenced as it.
• Useful for logging during chained calls.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.