java - 有没有一种方法可以有效地比较任意对象的字段

Question

目前，如果我需要通过特定字段比较对象，我会实现 DiffEqual 接口(interface)

interface DiffEquals<T> {
  fun isItemSame(other: Any?): Boolean
  fun isContentSame(other: Any?): Boolean
}

某个对象

data class Book(
  val title: String, val amount: String, var isSelected: Boolean = false
) : DiffEquals {

  override fun isItemSame(other: Any?): Boolean {
    if (other != null && other is Book) {
      if (title != other.title) {
        return false
      }
      return true
    } else {
      return false
    }
  }

  override fun isContentSame(other: Any?): Boolean {
    other as Book
    if (amount != other.amount) return false
    if (isSelected != other.isSelected) return false

    return true
  }
}

我不喜欢这种方法，因为它需要大量的虚拟代码。我尝试制作Id1、Id2、Id3、Mutable1、Mutable2、Mutable3等注释，但资源消耗很大，因此我不得不回滚到上面的界面。如何实现一种比较指定字段的通用比较机制？ (不是标准的 equals 不适合，因为更复杂的对象具有不断变化的字段，但对于相等并不重要，重写 equals 会与虚拟代码产生相同的问题，并且在大多数情况下，我需要完全等于)

Answer 1

您可以创建内联 equalsBy 函数:

@PublishedApi
@Suppress("UNCHECKED_CAST")
internal inline fun <T> T.eqlBy(other: Any?, prop1: T.() -> Any?): Boolean = prop1() == (other as T).prop1()

inline fun <reified T> T.equalsBy(other: Any?, prop1: T.() -> Any?): Boolean =
    other is T && eqlBy(other, prop1)

inline fun <reified T> T.equalsBy(other: Any?, prop1: T.() -> Any?, prop2: T.() -> Any?): Boolean =
    equalsBy(other, prop1) && eqlBy(other, prop2)

inline fun <reified T> T.equalsBy(other: Any?, prop1: T.() -> Any?, prop2: T.() -> Any?, prop3: T.() -> Any?): Boolean =
    equalsBy(other, prop1, prop2) && eqlBy(other, prop3)

像这样使用它们:

data class Book(
    val title: String, val amount: String, var isSelected: Boolean = false
) : DiffEquals<Book> {
    override fun isItemSame(other: Book) = equalsBy(other) { title }
    override fun isContentSame(other: Book) = equalsBy(other, { amount }, { isSelected })
}