可變和不可變集合類是相同的 kotlin

Question

當使用反射來調查集合類時，相同類型的可變類和不可變類在引用上是相等的。

為什么會這樣？

    @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映射到同一個 java.util.Collection class （映射類型），所以從 JVM 的 POV 來看，它們是相同的運行時。

如果你反編譯你寫的代碼，你會得到這個（我已經使用 Intellij 生成的 Kotlin 字節碼反編譯它）：

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);
}

參考：

• https://kotlinlang.org/docs/reference/java-interop.html#mapped-types
• （不可變集合是可變的）在 Kotlin 中返回 true
• Kotlin 使數據的構造函數 class 接受 List 和 MutableList 但存儲它們的可變實例