Smart cast to 'Type' is impossible, because 'x' is a mutable property that could have been changed by this time

So I run into this problem quite often lately, most of the time it happens when I have defined a Hibernate Entity in Kotlin, and I wish to use it in my code.

It happens when there's a property that could conceivably be accessed in another thread, cause the two statements, the if-statement and the execution statement to look at different states, and cause a ClassCastException.

The following code demonstrates the message Kotlin provides when writing such a program:

	private var name: String? = null
	/**
	* This does not compile, because after the if and before the assert, name could have been change
	* in another thread on this object.
	*/
	@Test
	fun mutablePropertyCouldHaveChanged1() {
	if (name != null) {
	// assertThat(name.length).isNotZero()
	}
	}

view raw MutablePropertyCouldHaveChanged1.kt hosted with ❤ by GitHub

Possible solutions

	/**
	* if we're sure, we can just brute-force is and tell Kotlin that we're sure the property is never null
	* here. I don't like this. Could be a thread-safety issue.
	*/
	@Test
	fun mutablePropertyCouldHaveChanged2() {
	if (name != null) {
	assertThat(name!!.length).isNotZero()
	}
	}

view raw MutablePropertyCouldHaveChanged2.kt hosted with ❤ by GitHub

	/**
	* create a local variabel so we're sure it is not a problem.
	*/
	@Test
	fun mutablePropertyCouldHaveChanged3() {
	val local = name
	if (local != null) {
	assertThat(local.length).isNotZero()
	}
	}

view raw MutablePropertyCouldHaveChanged3.kt hosted with ❤ by GitHub

	/**
	* use "?.let" to create a lambda in which we're sure there's no problem.
	* Is a very nice solution, if possible.
	*/
	@Test
	fun mutablePropertyCouldHaveChanged4() {
	name?.let { assertThat(it.length).isNotZero() }
	}

view raw MutablePropertyCouldHaveChanged4.kt hosted with ❤ by GitHub

References

Youtube - Let, Also, Apply, Run, With - Kotlin Scope Functions

https://www.youtube.com/watch?v=Vy-dS2SVoHk