run Scope Function in Kotlin

Introduction

run 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.

Run executes block with object as receiver (this). 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

• run executes block with object as receiver (this).
• Returns result of lambda.
• Useful for object configuration and computation.

Syntax

obj.run { ... }

run Scope Function in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val message = "kotlin".run {
        uppercase()
    }
    println(message)
}

Sample Output

KOTLIN

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 message = "kotlin".run { assigns or updates a value used later in the program.

3. The println(message) statement writes a line to the console — this produces part of the sample output below.

4. Run executes block with object as receiver (this).

5. 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: run executes block with object as receiver (this).
• 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

• run executes block with object as receiver (this).
• Returns result of lambda.
• Useful for object configuration and computation.
• 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.