isStableForSmartCasting¶

Whether this expression can be used as a stable smart-cast sink at the current program point.

Stability is only one prerequisite for applying a smart cast. A true result does not mean that the expression is currently smart-cast to a more specific type. It only means that data-flow facts about this expression may be applied if such facts are available.

This property is meaningful for expressions that can be represented as data-flow variables, such as local variables, parameters, receivers, and property accesses. It returns false for expressions that are not smart-cast sinks, such as literals, function calls, and other types of expressions.

Stable smart-cast sinks generally include:

• Local vals, value parameters, and stable receivers.

• Local vars that the compiler can treat as effectively immutable at this program point.

• val properties without delegation or custom getters, accessed through a stable receiver and declared in the current module.

Unstable smart-cast sinks generally include:

• Non-local var properties.

• Delegated properties.

• Properties with custom getters.

• Properties from separately compiled modules.

• open properties whose receiver is not known to have a final type.

• Local vars whose captured writes may invalidate the relevant data-flow facts.

See the Kotlin specification section on smart cast sink stability.

Example¶

class Container(val value: Any?)

open class OpenContainer(open val value: Any?)

fun source(): Any? = ""

fun test(container: Container, openContainer: OpenContainer) {
    val local: Any? = ""
    var mutableLocal: Any? = ""
    mutableLocal = "tracked assignment"

    // local.isStableForSmartCasting == true
    // mutableLocal.isStableForSmartCasting == true
    // container.value.isStableForSmartCasting == true
    // openContainer.value.isStableForSmartCasting == false
    // source().isStableForSmartCasting == false
}