kotlin - 可变和不可变集合类是同一个 kotlin

Question

当使用反射来调查集合类时，同一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)}")
    }

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被映射到同一个 java.util.Collection 类(mapped-types)，所以从 JVM 的 POV(在运行时编译之后)来看它们是相同的。
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 Bytecode 反编译了它):
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);
}

引用:

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

(imutable collection is mutable) returns true in Kotlin

Kotlin make constructor of data class accept both List and MutableList but store a mutable instance of them