In Kotlin, the safe call operator ?. lets you access a property or call a function only if the value is not null.

If the value is null, the expression simply returns null instead of throwing a NullPointerException.

val name: String? = null

val length = name?.length

println(length) // null

Here, name is nullable because its type is String?. Since name is null, name?.length does not try to access .length; it returns null.

Basic syntax

nullableValue?.property
nullableValue?.function()

Example:

val user: User? = getUser()

val email = user?.email

If user is not null, email gets user.email.

If user is null, email becomes null.

Chaining safe calls

You can chain multiple safe calls together:

val city = user?.address?.city

This means:

• if user is null, return null
• otherwise check address
• if address is null, return null
• otherwise return city

Using ?. with a default value

Often, you combine ?. with the Elvis operator ?::

val length = name?.length ?: 0

This means:

• if name is not null, use name.length
• if name is null, use 0

Using ?.let

Use ?.let when you want to run code only when a value is not null:

val name: String? = "Kotlin"

name?.let {
    println("Name is $it")
    println("Length is ${it.length}")
}

The block runs only if name is not null.

Safe call on assignment

Safe calls can also be used on the left side of an assignment:

person?.address?.city = "Paris"

If person or address is null, the assignment is skipped.

Summary

val result = nullableValue?.someProperty

Use ?. when:

• a value might be null
• you want to avoid NullPointerException
• returning null is acceptable when the receiver is null

Common pattern:

val result = nullableValue?.someProperty ?: defaultValue