Type inference by the compiler in Kotlin

Introduction

Type inference helps the compiler guess the type of a value so you don't have to write it every time. This makes your code shorter and easier to read.

When you want to declare a variable without writing its type explicitly.

When you assign a value to a variable and want the compiler to figure out its type.

When you want cleaner code without losing type safety.

When working with functions that return values and you want the compiler to know the return type.

When you want to avoid clutter in your code but still keep it safe.

Syntax

Kotlin

val variableName = value
var variableName = value

The compiler looks at the value on the right side and decides the type automatically.

Use val for read-only variables and var for variables that can change.

Examples

The compiler knows number is an Int because 10 is an integer.

Kotlin

val number = 10

The compiler infers name is a String from the text in quotes.

Kotlin

val name = "Alice"

Here, price is a Double because 9.99 is a decimal number.

Kotlin

var price = 9.99

The compiler infers isActive is a Boolean from the value true.

Kotlin

val isActive = true

Sample Program

This program shows variables declared without explicit types. The compiler figures out the types from the assigned values.

Kotlin

fun main() {
    val age = 25
    val greeting = "Hello, Kotlin!"
    var temperature = 36.6
    val isSunny = false

    println("Age: $age")
    println("Greeting: $greeting")
    println("Temperature: $temperature")
    println("Is it sunny? $isSunny")
}

Important Notes

Type inference does not mean the compiler guesses randomly; it uses the value's type to decide.

If you want, you can still write the type explicitly for clarity, like val age: Int = 25.

Type inference works well with simple assignments but sometimes you need to specify types for complex cases.

Summary

Type inference lets the compiler find out variable types automatically.

It makes code shorter and easier to read without losing safety.

Use it when you assign values directly to variables.