with Scope Function in Kotlin

Introduction

with 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.

With is a non-extension function that calls block on 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

• with is a non-extension function that calls block on object.
• Inside block, object is available as this.
• Returns result of lambda.

Syntax

with(obj) { ... }

with Scope Function in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val person = mutableMapOf("name" to "Riya", "city" to "Chennai")
    val info = with(person) {
        put("country", "India")
        this
    }
    println(info)
}

Sample Output

{name=Riya, city=Chennai, country=India}

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 person = mutableMapOf("name" to "Riya", "city" to "Chennai") assigns or updates a value used later in the program.

3. val info = with(person) { assigns or updates a value used later in the program.

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

5. With is a non-extension function that calls block on 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: with is a non-extension function that calls block on 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

• with is a non-extension function that calls block on object.
• Inside block, object is available as this.
• Returns result of lambda.
• 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.