如何安全地解决初始值设定项中的空检查？

Question

我正在写一个测试用例，我需要一些私有属性。由于这些私有数据是从私有方法生成的，所以我决定在计算完成后使用反射来检索它们。后来，我想起了委托的属性，并决定编写一个通用委托。以下是我目前得到的代码：

fun <T> reflect(instance: Any, initOnce: Boolean = true) = ReflectBackedProperty<T>(initOnce, instance)

class ReflectBackedProperty<T>(val initOnce: Boolean, val instance: Any): ReadOnlyProperty<Any, T>  {
    var initialized = false
    lateinit var cache: T // <--- (a)
    override opertaor fun getValue(thisRef: Any, property: KProperty<*>): Any? {
        @Suppress("UNCHECKED_CAST")
        if (!initialized || !initOnce) {
            cache = instance.javaClass.getDeclaredField(property.name).get(instance) as T
            initialized = true
        }
        return cache
    }
}

Kthacks.java

public final class KTHacks {
    private KTHacks() {
        throw new UnsupportedOperationException();
    }

    /**
     * Forge a null into a platform type and take advantage of relaxed null-checks.
     * @param <T>
     * @return
     */
    public static <T> T NULL() {
        return null;
    }
}

ReflectBakedProperty.kt

import kotlin.properties.ReadOnlyProperty
import kotlin.reflect.KProperty

fun <T> reflect(instance: Any, initOnce: Boolean = true) = ReflectBackedProperty<T>(initOnce, instance)

class ReflectBackedProperty<T>(val initOnce: Boolean, val instance: Any): ReadOnlyProperty<Any, T> {
    var initialized = false
    var cache: T = KTHacks.NULL()
    override operator fun getValue(thisRef: Any, property: KProperty<*>): T {
        @Suppress("UNCHECKED_CAST")
        if (!initialized || !initOnce) {
            cache = instance.javaClass.getDeclaredField(property.name).get(instance) as T
            initialized = true
        }
        return cache
    }
}

Answer 1

一种方法是将t限制为仅允许具有上限的不可空类型：

class ReflectBackedProperty<T: Any> : ReadOnlyProperty<Any, T> {}

另一种方法是根本不需要使用lateinit：

class ReflectBackedProperty<T>(val initOnce: Boolean, val instance: Any): ReadOnlyProperty<Any, T>  {
    var initialized = false
    var cache: T? = null

    override operator fun getValue(thisRef: Any, property: KProperty<*>): T {
        if (!initialized || !initOnce) {
            cache = instance.javaClass.getDeclaredField(property.name).get(instance) as T
            initialized = true
        }
        return cache as T
    }
}