Kotlin approach to syntactically local static caching

Static.kt

import java.util.concurrent.atomic.AtomicReference

private val cache = object : ClassValue<AtomicReference<Any?>>() {
    override fun computeValue(type: Class<*>) = AtomicReference<Any?>()
}

/**
 * Caches the given expression statically.
 *
 * Use it like this:
 * ```
 * static { expr() }.thing()
 * ```
 *
 * See https://twitter.com/lukaseder/status/917677218679214080
 */
@Suppress("UNCHECKED_CAST")
public fun <T : Any> static(expr: () -> T): T {
    val clazz = expr::class.java
    val ref = cache[clazz]
    ref.get()?.let { return it as T }
    // using double-checked locking to ensure at most one invocation of expr
    synchronized(clazz) {
        ref.get()?.let { return it as T }
        val value = expr()
        ref.set(value)
        return value
    }
}