如果kotlin已经有了getter和setter，为什么在数据类中有componentN函数

发布于04月01日

kotlin中有一个数据类，例如.

@Entity
data class Record(
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    val id: Long? = null,
    @Column(nullable = false, name = "name")
    var name: String? = null
)

And I can call component1 and component2 functions to access the properties. However, as I declare the property var, I have getter and setter, and if I declare property val I have the getter. Are componentN functions are redundant in this case, and why do we need them, because getters seem to be much more self-explanatory?

推荐答案

Kotlin通过componentN个函数支持以下语法:

val (name, age) = person

这种语法称为destructuring declaration.析构声明一次创建多个变量.我们声明了两个新变量:name和age.

A destructuring declaration is compiled down to the following code:

val name = person.component1()
val age = person.component2()

the component1() and component2() functions are another example of the principle of conventions widely used in Kotlin (see operators like + and *, for-loops etc.). Anything can be on the right-hand side of a destructuring declaration, as long as the required number of component functions can be called on it. And, of course, there can be component3() and component4() and so on.

Note that the componentN() functions need to be marked with the operator keyword to allow using them in a destructuring declaration.