如何通过反射收集成员以稍后作为参数传递

Question

所以，我正在研究一个概念，涉及自动写入 ByteBuffer 扩展 Bufferizable

的 class 的内容

abstract class Bufferizable {

    abstract val fieldOrder: Array<String>

    open fun size(): Int = TODO()

    var initialized = false

    open infix fun to(address: Long) {

        if (initialized) {

            addFunctions.forEach {  }

        } else {

            addFunctions = Array(fieldOrder.size) { null }
            members = Array(fieldOrder.size) { null }

            fieldOrder.forEachIndexed { i, field ->
                val member = this::class.declaredMemberProperties.find { it.name == field }!!
                addFunctions[i] = when (member.returnType) {
                    Mat4::class.defaultType.javaType -> WithAddress::addMat4
                    ...
                    else -> throw Error()
                } as BufferizableAddFunctionType
                members[i] = member.get(this) // error
            }

            initialized = true
        }
    }

    infix fun from(address: Long): Unit = TODO()

    var addFunctions = arrayOf<BufferizableAddFunctionType?>()
    var members = arrayOf<Any?>()
}

typealias BufferizableAddFunctionType = (Any) -> Unit

object WithAddress {

    var address = NULL
    var offset = 0

    fun addMat4(mat4: Mat4) {
        for (i in 0..3)
            for (j in 0..3) {
                memPutFloat(address + offset, mat4[i, j])
                offset += Float.BYTES
            }
    }
    ...
}

思路就是声明，比如下面这样

object uboVS : Bufferizable() {

    var projectionMatrix = Mat4()
    var modelMatrix = Mat4()
    ...

    override val fieldOrder = arrayOf("projectionMatrix", "modelMatrix", "viewMatrix")
}

然后每当 uboVS to address 第一次被调用时，它会被初始化，然后按照指定的顺序将其内容写入本机地址。

但我遇到的唯一问题是收集成员以作为参数传递给第 i 个 addFunction

因为编译器在这里报错：

members[i] = member.get(this)

Error:(328, 37) Kotlin: Out-projected type 'KProperty1' prohibits the use of 'public abstract fun get(receiver: T): R defined in kotlin.reflect.KProperty1'

我该如何解决？

Answer 1

这是一个继承问题。您的反射调用 this::class.declaredMemberProperties.find{ ... } returns a KProperty1<out Bufferizable, Any?> 这意味着属性来自继承自 Bufferizable 的东西（有关 out 的更多信息，请参阅 declaration-site variance） .通过编译器不知道这个属性属于哪个 class 它不允许直接访问。要解决此问题，您必须访问 getter 函数：

members[i] = member.getter.call(this)

通过getter函数属于对象不属于反射api遵循默认的继承行为，可以调用

如何通过反射收集成员以稍后作为参数传递

How to collect members via reflection to pass as argument later

reflection

kotlin

kotlin-reflect