可变和不可变集合类是相同的 kotlin

Question

当使用反射来调查集合类时，相同类型的可变类和不可变类在引用上是相等的。

为什么会这样？

    @Test
    fun demonstrate_mutableAndImmutableClassesAreTheSame() {
        println("(MutableIterable::class === Iterable::class) = ${(MutableIterable::class === Iterable::class)}")
        println("(MutableCollection::class === Collection::class) = ${(MutableCollection::class === Collection::class)}")
        println("(MutableList::class === List::class) = ${(MutableList::class === List::class)}")
        println("(MutableSet::class === Set::class) = ${(MutableSet::class === Set::class)}")
        println("(MutableMap::class === Map::class) = ${(MutableMap::class === Map::class)}")
        println("(MutableMap.MutableEntry::class === Map.Entry::class) = ${(MutableMap.MutableEntry::class === Map.Entry::class)}")
    }

印刷

(Iterable::class === MutableIterable::class) = true
（集合::class === MutableCollection::class）= true
(列表::class === MutableList::class) = true
(集::class === MutableSet::class) = true

Answer 1

Collection和MutableCollection映射到同一个 java.util.Collection class （映射类型），所以从 JVM 的 POV 来看，它们是相同的运行时。

如果你反编译你写的代码，你会得到这个（我已经使用 Intellij 生成的 Kotlin 字节码反编译它）：

Kotlin：

fun demonstrate_mutableAndImmutableClassesAreTheSame() {
    println("(MutableCollection::class === Collection::class) = ${(MutableCollection::class === Collection::class)}")
}

Java：

import kotlin.jvm.internal.Reflection;

// class declaration
public static final void demonstrate_mutableAndImmutableClassesAreTheSame() {
    String var0 = "(MutableCollection::class === Collection::class) = " + (Reflection.getOrCreateKotlinClass(Collection.class) == Reflection.getOrCreateKotlinClass(Collection.class));
    boolean var1 = false;
    System.out.println(var0);
}

参考：

• https://kotlinlang.org/docs/reference/java-interop.html#mapped-types
• （不可变集合是可变的）在 Kotlin 中返回 true
• Kotlin 使数据的构造函数 class 接受 List 和 MutableList 但存储它们的可变实例