可变和不可变集合 类 是同一个 kotlin

Question

当使用反射来研究集合 类 时，同一类型的可变和不可变 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)}")
    }

打印

(Iterable::class === MutableIterable::class) = true
(Collection::class === MutableCollection::class) = true
(List::class === MutableList::class) = true
(Set::class === MutableSet::class) = true

Answer 1

Collection 和 MutableCollection 映射到相同的 java.util.Collection class （映射类型），因此从 JVM 的 POV（在运行时编译后）来看，它们都一样。

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

科特林：

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);
}

参考文献：

• https://kotlinlang.org/docs/reference/java-interop.html#mapped-types