Kotlin数据类上的属性包括/排除
假设我只希望在生成的equals和hashCode实现中包含一个或两个字段(或者排除一个或多个字段)。对于简单类,例如:Kotlin数据类上的属性包括/排除,kotlin,reflection,annotations,data-class,Kotlin,Reflection,Annotations,Data Class,假设我只希望在生成的equals和hashCode实现中包含一个或两个字段(或者排除一个或多个字段)。对于简单类,例如: data class Person(val id: String, val name: String) Groovy有以下特点: @EqualsAndHashCode(includes = 'id') @EqualsAndHashCode(of = "id") 龙目岛有: @EqualsAndHashCode(includes = 'id') @E
data class Person(val id: String, val name: String)
Groovy有以下特点:
@EqualsAndHashCode(includes = 'id')
@EqualsAndHashCode(of = "id")
龙目岛有:
@EqualsAndHashCode(includes = 'id')
@EqualsAndHashCode(of = "id")
Kotlin的惯用做法是什么
我目前的做法
只是感觉不对。。。我真的不希望
name
是可变的,而且额外的构造函数定义很难看。这里有一个有点创造性的方法:
data class IncludedArgs(val args: Array<out Any>)
fun includedArgs(vararg args: Any) = IncludedArgs(args)
abstract class Base {
abstract val included : IncludedArgs
override fun equals(other: Any?) = when {
this identityEquals other -> true
other is Base -> included == other.included
else -> false
}
override fun hashCode() = included.hashCode()
override fun toString() = included.toString()
}
class Foo(val a: String, val b : String) : Base() {
override val included = includedArgs(a)
}
fun main(args : Array<String>) {
val foo1 = Foo("a", "b")
val foo2 = Foo("a", "B")
println(foo1 == foo2) //prints "true"
println(foo1) //prints "IncludedArgs(args=[a])"
}
包含参数的数据类(val-args:Array)
fun includedArgs(vararg-args:Any)=includedArgs(args)
抽象类基{
包含的抽象值:IncludedArgs
覆盖乐趣等于(其他:任何?)=何时{
此标识等同于其他->真
其他为基础->包含==其他。包含
else->false
}
重写fun hashCode()=包含的.hashCode()
重写fun-toString()=包含的.toString()
}
类Foo(val a:String,val b:String):Base(){
覆盖val included=includedArgs(a)
}
趣味主线(args:Array){
val foo1=Foo(“a”、“b”)
val foo2=Foo(“a”、“B”)
println(foo1==foo2)//打印“true”
println(foo1)//打印“IncludedArgs(args=[a])”
}
我也不知道Kotlin(1.1)中的“idomatic方式”如何做到这一点
我最终覆盖了equals
和hashCode
:
data class Person(val id: String,
val name: String) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other?.javaClass != javaClass) return false
other as Person
if (id != other.id) return false
return true
}
override fun hashCode(): Int {
return id.hashCode()
}
}
难道没有“更好”的方法吗?我用过这种方法
data class Person(val id: String, val name: String) {
override fun equals(other: Person) = EssentialData(this) == EssentialData(other)
override fun hashCode() = EssentialData(this).hashCode()
override fun toString() = EssentialData(this).toString().replaceFirst("EssentialData", "Person")
}
private data class EssentialData(val id: String) {
constructor(person: Person) : this(id = person.id)
}
这基于@bashor的方法,并使用私有主构造函数和公共辅助构造函数。遗憾的是,equals要忽略的属性不能是val,但可以隐藏setter,因此从外部角度来看,结果是等效的
data class ExampleDataClass private constructor(val important: String) {
var notSoImportant: String = ""
private set
constructor(important: String, notSoImportant: String) : this(important) {
this.notSoImportant = notSoImportant
}
}
可重用解决方案:为了有一个简单的方法来选择在
equals()
和hashCode()
中包含哪些字段,我编写了一个名为“stem”(与相等相关的基本核心数据)的小助手
使用非常简单,生成的代码非常小:
class Person(val id: String, val name: String) {
private val stem = Stem(this, { id })
override fun equals(other: Any?) = stem.eq(other)
override fun hashCode() = stem.hc()
}
可以通过动态的额外计算来权衡类中存储的支持字段:
private val stem get() = Stem(this, { id })
由于Stem
接受任何函数,因此您可以自由指定等式的计算方式。对于要考虑的多个字段,只要添加每个字段的一个lambda表达式(VARARGS):
实施:
class Stem<T : Any>(
private val thisObj: T,
private vararg val properties: T.() -> Any?
) {
fun eq(other: Any?): Boolean {
if (thisObj === other)
return true
if (thisObj.javaClass != other?.javaClass)
return false
// cast is safe, because this is T and other's class was checked for equality with T
@Suppress("UNCHECKED_CAST")
other as T
return properties.all { thisObj.it() == other.it() }
}
fun hc(): Int {
// Fast implementation without collection copies, based on java.util.Arrays.hashCode()
var result = 1
for (element in properties) {
val value = thisObj.element()
result = 31 * result + (value?.hashCode() ?: 0)
}
return result
}
@Deprecated("Not accessible; use eq()", ReplaceWith("this.eq(other)"), DeprecationLevel.ERROR)
override fun equals(other: Any?): Boolean =
throw UnsupportedOperationException("Stem.equals() not supported; call eq() instead")
@Deprecated("Not accessible; use hc()", ReplaceWith("this.hc(other)"), DeprecationLevel.ERROR)
override fun hashCode(): Int =
throw UnsupportedOperationException("Stem.hashCode() not supported; call hc() instead")
}
如果这些方法是隐式调用或通过反射调用的,那么异常只是一种回退;如果有必要,可以进行辩论
当然,
Stem
类可以进一步扩展,以包括自动生成toString()
等。此方法可能适用于属性排除:
class SkipProperty<T>(val property: T) {
override fun equals(other: Any?) = true
override fun hashCode() = 0
}
您可以通过定义enum,创建一个将属性排除表示为@ExcludeToString
或带有@ToString(Type.EXCLUDE)
参数的
然后使用格式设置getToString()
的值
@Target(AnnotationTarget.FIELD)
@保留(AnnotationRetention.RUNTIME)
注释类ExcludeToString
数据类测试(
var a:String=“测试a”,
@ExcludeToString变量b:String=“测试b”
) {
重写funtostring():String{
返回ExcludeToString.getToString(此)
}
}
对象排除字符串{
有趣的getToString(对象:任意):字符串{
val-toString=LinkedList()
getFieldsNotExludeToString(obj).forEach{prop->
prop.isAccessible=true
toString+=“${prop.name}=“+prop.get(obj)?.toString()?.trim()
}
返回“${obj.javaClass.simpleName}=[${toString.joinToString(“,”)}”
}
私人娱乐getFieldsNotExludeToString(对象:任意):列表{
val declaredFields=obj::class.java.declaredFields
返回declaredFields.filterNot{field->
isFieldWithExludeToString(字段)
}
}
private fun isFieldWithExludeToString(字段:字段):布尔值{
field.annotations.forEach{
if(it.annotationClass==ExcludeToString::class){
返回真值
}
}
返回错误
}
}
德国劳埃德船级社
更简单、更快,请查看此处或Kotlin文档。
只有主构造函数中的字段才会被考虑来构建自动访问方法,比如equals等等。把那些没有意义的东西放在外面。有趣的解决办法!我个人不会交换几行样板赋值,例如@bashor示例中的
val name:String=name
,用于从Base
类继承,以弥补缺少的语言特性。我同意,我的解决方案不是很优雅。我只是为了好玩而把它拼凑在一起,并决定与大家分享。我认为我的解决方案也不完美,但有一些好处。看看。equals应该覆盖“Any?”这看起来有点麻烦。这仍然是最新的最佳解决方案吗?equals
fun的改进:override-fun-equals(other:Any?):Boolean{if(other!=Person)return false-return-EssentialData(this)==EssentialData(other)}
编写@dstibbe改进的更惯用方法是:override-fun-equals(other:Any?)=other is Person&&EssentialData(this)==EssentialData(other)
Nice improvement@KristopherNoronha。这很有创意,因此+1是一种解决方案,但这不是我会采用的解决方案。对字段的任何访问都有额外的.property
,该字段缺少对其包含类的equals/hashCode的参与,这只是该类的一个实现细节。当然,您可以在该属性上重写get()/set()
,以自动执行此操作,但是ooof。对这样的要求来说很重。是的,你是对的。我只想分享我的尝试。很有趣,谢谢。我会试试的!
class SkipProperty<T>(val property: T) {
override fun equals(other: Any?) = true
override fun hashCode() = 0
}
data class Person(
val id: String,
val name: SkipProperty<String>
)
@Target(AnnotationTarget.FIELD)
@Retention(AnnotationRetention.RUNTIME)
annotation class ExcludeToString
data class Test(
var a: String = "Test A",
@ExcludeToString var b: String = "Test B"
) {
override fun toString(): String {
return ExcludeToStringUtils.getToString(this)
}
}
object ExcludeToStringUtils {
fun getToString(obj: Any): String {
val toString = LinkedList<String>()
getFieldsNotExludeToString(obj).forEach { prop ->
prop.isAccessible = true
toString += "${prop.name}=" + prop.get(obj)?.toString()?.trim()
}
return "${obj.javaClass.simpleName}=[${toString.joinToString(", ")}]"
}
private fun getFieldsNotExludeToString(obj: Any): List<Field> {
val declaredFields = obj::class.java.declaredFields
return declaredFields.filterNot { field ->
isFieldWithExludeToString(field)
}
}
private fun isFieldWithExludeToString(field: Field): Boolean {
field.annotations.forEach {
if (it.annotationClass == ExcludeToString::class) {
return true
}
}
return false
}
}