Kotlin 数据类可选变量

发布于11月06日

data class Student(
    val id: Int?,
    val firstName: String?,
    val lastName: String?,
    val hobbyId: Int?,
    val address1: String?,
    val address2: String?,
    val created: String?,
    val updated: String?,
    ...
)

我喜欢上面的数据类，我想创建一个只有名字和姓氏的学生实例.

// creating a student 
Student(
    firstName = "Mark"
    lastName = "S"
)

I will get No value passed for parameter 'id' ... errors.

To avoid that, I modified the Student class like this,

data class Student(
    val id: Int? = null,
    val firstName: String? = null,
    val lastName: String? = null,
    val hobbyId: Int? = null,
    val address1: String? = null,
    val address2: String? = null,
    val created: String? = null,
    val updated: String? = null,
    ...
)

But it looks so ugly.

Is there any better way?

推荐答案

我不确定我给你的解决方案是不是最好的.但绝对是整洁的.

The only thing I don't like to go with nulls as default param, because Kotlin offers Null Safety, lets not remove it just because to fulfil some other requirement. Mark them null only if they can be null. Else old Java way is good. Initialize them with some default value.

data class Student(val id: Int,
                   val firstName: String,
                   val lastName: String,
                   val hobbyId: Int,
                   val address1: String,
                   val address2: String,
                   val created: String,
                   val updated: String) {
    constructor(firstName: String, lastName: String) :
            this(Int.MIN_VALUE, firstName, lastName, Int.MIN_VALUE, "", "", "", "")
}