How to use Kotlin's `with` expression for nullable types

Question

The code below will not compile because the variable myType can be null. Is there a way of executing a with block for nullable types in Kotlin?

    val myType: MyType? = null
    with(myType) {
        aMethodThatBelongsToMyType()
        anotherMemberMethod()            
    }

Answer 1

You can convert a nullable type to a non-nullable type with the suffix !!:

with(myType!!) {
    aMethodThatBelongsToMyType()
    anotherMemberMethod()            
}

If the value is indeed null, it will throw a NullPointerException, so this should generally be avoided.

A better way to do this is to make the execution of the code block dependent on the value being non-null by making a null-safe call and using the apply extension function instead of with:

myType?.apply {
    aMethodThatBelongsToMyType()
    anotherMemberMethod()            
}

Yet another option is to check if the value is non-null with an if statement. The compiler will insert a smart cast to a non-nullable type inside the if-block:

if (myType != null) {
    with(myType) {
        aMethodThatBelongsToMyType()
        anotherMemberMethod()            
    }
}