How to Use with Function in Kotlin: Simple Guide

In Kotlin, the with function lets you call multiple methods or access properties on the same object without repeating its name. You pass the object and a block of code where you can use its members directly, making your code cleaner and easier to read.

Syntax

The with function takes two parts: the object you want to work with, and a block of code where you can call the object's methods or properties directly.

Syntax:

with(object) {
    // code using object members
}

Inside the block, this refers to the object, so you don't need to repeat the object name.

kotlin

with(receiverObject) {
    // use receiverObject's methods or properties here
}

Example

This example shows how to use with to print details of a StringBuilder object without repeating its name.

kotlin

fun main() {
    val sb = StringBuilder()
    with(sb) {
        append("Hello")
        append(", ")
        append("Kotlin!")
        println(toString())
    }
}

Output

Hello, Kotlin!

Common Pitfalls

One common mistake is trying to use with when you need to return a value from the block. with returns the last expression, but if you don't use it properly, you might ignore the result.

Also, avoid using with on null objects, as it will cause a NullPointerException.

kotlin

fun main() {
    val list = listOf(1, 2, 3)

    // Wrong: ignoring the return value of with
    with(list) {
        println(size)
    }

    // Right: using the return value
    val size = with(list) {
        size
    }
    println("Size is $size")
}

Output

3
Size is 3

Quick Reference

• Purpose: Call multiple methods on the same object without repeating its name.
• Returns: The last expression inside the block.
• Receiver: The object passed as the first argument.
• Use case: Simplify code readability.

Key Takeaways

Use with to call multiple methods on one object without repeating its name.

with returns the last expression inside its block, so you can capture results.

Avoid using with on null objects to prevent errors.

Inside with, this refers to the object, allowing direct access to its members.

Use with to make your code cleaner and more readable when working with one object.