Kotlin中调用超类构造函数，Super不是表达式

代码中有几个问题.

首先，这是从二级构造函数调用超级构造函数的正确语法:

constructor(entity: Entity) : super(entity)

其次，如果你的类有primary constructor(你的类有primary constructor)，你不能从secondary构造函数调用超级构造函数.

Solution 1

abstract class Entity(
        var id: String,
        var created: Date
)

class Account(
        var name: String,
        var accountFlags: Int,
        id: String,
        created: Date
) : Entity(id, created) {
    constructor(account: Account) : this(account.name, account.accountFlags, account.id, account.created)
}

这里，复制构造函数位于子类中，该子类只委托给主构造函数.

解决方案2

abstract class Entity(
        var id: String,
        var created: Date
) {
    constructor(entity: Entity) : this(entity.id, entity.created)
}

class Account : Entity {
    var name: String
    var accountFlags: Int

    constructor(name: String, accountFlags: Int, id: String, created: Date) : super(id, created) {
        this.name = name
        this.accountFlags = accountFlags
    }

    constructor(account: Account) : super(account) {
        this.name = account.name
        this.accountFlags = account.accountFlags
    }
}

Here I'm only using secondary constructors in the child class which lets me delegate them to individual super constructors. Notice how the code is pretty long.

解决方案3(最惯用)

abstract class Entity {
    abstract var id: String
    abstract var created: Date
}

data class Account(
        var name: String,
        var accountFlags: Int,
        override var id: String,
        override var created: Date
) : Entity()

在这里，我省略了复制构造函数，并将属性抽象化，这样子类就拥有了所有属性.我还让这个子元素上了data class级.如果需要克隆该类，只需调用account.copy()即可.