CODEWITHSUNDEEP
kotlin
Alexey
Alexey

Reputation: 3192

Kotlin smart cast not working with extensions functions

I am trying check nullable object with extension function, but smart casting not work after calling this function.

fun <T> T?.test(): T = this ?: throw Exception()

val x: String? = "x"
x.test()
x.length // Only safe (?.) or non-null asserted (!!) calls are allowed on a nullable receiver of type String?

Is it a Kotlin bug? If not, why there is no implicit casting?

Upvotes: 3

Views: 1646

Answers (1)

Niroshan
Niroshan

Reputation: 1282

As @Madhu Bhat mentioned in comment above, your variable 'x' is still nullable. You may use your function simply like this:

x.test().length

Otherwise you can check for null by following inline function and then perform any functions directly on the variable. (Note the usage of 'contract' and annotations '@ExperimentalContracts')

@ExperimentalContracts
fun <T> T?.notNull(): Boolean {

    contract {
        returns(true) implies (this@notNull != null)
    }

    return this != null
}

Now you can use this function like this

if(x.notNull()){
  x.length
}

But its not seems so useful if your using this function just to check nullability.

Check here to know more about Kotlin contracts

Upvotes: 3

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