java Kotlin 属性的私有 getter 和公共 setter
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Private getter and public setter for a Kotlin property
提问by Randy Sugianto 'Yuku'
How to make a property in Kotlin that has a private getter (or just do not have it) but has a public setter?
如何在 Kotlin 中创建具有私有 getter（或只是没有它）但具有公共 setter 的属性？
var status
private get
doesn't work with an error: Getter visibility must be the same as property visibility
不会出现错误： Getter visibility must be the same as property visibility
In my case, the reason is for Java interop: I want my Java code to be able to call setStatusbut not getStatus.
就我而言，原因是 Java 互操作：我希望我的 Java 代码能够调用setStatus但不能调用getStatus.
采纳答案by Alexander Udalov
It's impossible at the moment in Kotlin to have a property with a setter that is more visible than the property. There's a language design issue in the issue tracker on this, feel free to watch/vote for it or share your use cases: https://youtrack.jetbrains.com/issue/KT-3110
目前在 Kotlin 中不可能有一个属性的 setter 比属性更明显。问题跟踪器中存在一个语言设计问题，请随时观看/投票或分享您的用例：https: //youtrack.jetbrains.com/issue/KT-3110
回答by miensol
In current Kotlin version (1.0.3) the only option is to have separate settermethod like so:
在当前的 Kotlin 版本 (1.0.3) 中，唯一的选择是使用单独的setter方法，如下所示：
class Test {
private var name: String = "name"
fun setName(name: String) {
this.name = name
}
}
If you wish to restrict external libraries from accessing the getter you can use internalvisibility modifier allowing you to still use property syntax within the library:
如果您希望限制外部库访问 getter，您可以使用internal可见性修饰符，允许您仍然在库中使用属性语法：
class Test {
internal var name: String = "name"
fun setName(name: String) { this.name = name }
}
fun usage(){
val t = Test()
t.name = "New"
}
回答by TheOperator
Write-only properties with compile-time errors canbe achieved since Kotlin 1.0, using a workaround based on @Deprecated.
编译时错误只写性能可以因为科特林1.0来实现，使用基于一种变通方法@Deprecated。
Implementation
执行
Kotlin allows to mark functions deprecated with level ERROR, which leads to a compile-time error when called. Annotating the getaccessor of a property as error-deprecated, combined with a backing field (so that private reads are still possible), achieves the desired behavior:
Kotlin 允许使用 level 标记不推荐使用的函数ERROR，这会在调用时导致编译时错误。get将属性的访问器注释为error-deprecated，结合支持字段（以便私有读取仍然可能），实现了所需的行为：
class WriteOnly {
private var backing: Int = 0
var property: Int
@Deprecated("Property can only be written.", level = DeprecationLevel.ERROR)
get() = throw NotImplementedError()
set(value) { backing = value }
val exposed get() = backing // public API
}
Usage:
用法：
val wo = WriteOnly()
wo.property = 20 // write: OK
val i: Int = wo.property // read: compile error
val j: Int = wo.exposed // read value through other property
The compile error is quite helpful, too:
编译错误也很有帮助：
Using 'getter for property: Int' is an error. Property can only be written.
使用 'getter for property: Int' 是一个错误。属性只能写。
Use cases
用例
The main use case are obviously APIs that allow properties to be written, but not read:
user.password = "secret" val pw = user.password // forbiddenAnother scenario is a property which modifies the internal state, but is not stored itself as a field. (Could be done more elegantly using different design).
body.thrust_force = velocity body.gravity_force = Vector(0, 0, 9.8) // only total force accessible, component vectors are lost val f = body.forcesThis pattern is also useful for DSLs of the following kind:
server { port = 80 host = "www.example.com" }In such cases, values are simply used as one-time settings, and the write-only mechanism described here can prevent accidentally reading a property (which might not be initialized yet).
主要用例显然是允许写入但不允许读取属性的 API：
user.password = "secret" val pw = user.password // forbidden另一种情况是修改内部状态的属性，但它本身不存储为字段。（可以使用不同的设计更优雅地完成）。
body.thrust_force = velocity body.gravity_force = Vector(0, 0, 9.8) // only total force accessible, component vectors are lost val f = body.forces此模式对于以下类型的 DSL 也很有用：
server { port = 80 host = "www.example.com" }在这种情况下，值仅用作一次性设置，此处描述的只写机制可以防止意外读取属性（可能尚未初始化）。
Limitations
限制
Since this feature was not designed for this use case, it comes with certain limitations:
由于此功能不是为此用例设计的，因此具有某些限制：
If accessed using a property reference, the compile-time error turns into a runtime error:
val ref = wo::property val x = ref.get() // throws NotImplementedErrorThe same is true for reflection.
This functionality cannot be outsourced into a delegate, because an error-deprecated
getValue()method cannot be used withby.
如果使用属性引用访问，编译时错误会变成运行时错误：
val ref = wo::property val x = ref.get() // throws NotImplementedError反射也是如此。
此功能不能外包给委托，因为错误弃用的
getValue()方法不能与by.
