Inout 不使用 SubClass 对象抛出无法将不可变值作为 inout 参数传递

Question

我有两段代码

func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
  // BLOCK 1 Which is not working 
    guard let planeAnchor = anchor as? ARPlaneAnchor else { return }

    var plane = Plane(with: planeAnchor) //IT IS SUBCLASS OF SCNNode
    var geo = plane.geometry
    plane.transform = SCNMatrix4MakeRotation(-.pi / 2, 1, 0, 0)

    update(&plane, withGeometry: plane.geo, type: .static)

   //Up here Cannot pass immutable value as inout argument: implicit conversion from 'Plane' to 'SCNNode' requires a temporary

    node.addChildNode(plane)

   // BLOCK 2 Which is working 


    let width = CGFloat(planeAnchor.extent.x)
    let height = CGFloat(planeAnchor.extent.z)
    let plane1 = SCNPlane(width: width, height: height)

    plane1.materials.first?.diffuse.contents = UIColor.white.withAlphaComponent(0.5)

    var planeNode = SCNNode(geometry: plane1)

    let x = CGFloat(planeAnchor.center.x)
    let y = CGFloat(planeAnchor.center.y)
    let z = CGFloat(planeAnchor.center.z)
    planeNode.position = SCNVector3(x,y,z)
    planeNode.eulerAngles.x = -.pi / 2

    update(&planeNode, withGeometry: plane1, type: .static)
    // WORKING FINE

    node.addChildNode(planeNode)

    self.planes[anchor.identifier] = plane

}

BLOCK1

我有子类 class Plane: SCNNode 当我尝试将它的对象传递给需要 inout 的函数时它显示错误

Cannot pass immutable value as inout argument: implicit conversion from 'Plane' to 'SCNNode' requires a temporary

虽然如果我删除子类那么它工作正常

为什么这是 swift 错误或者我遗漏了什么？

Answer 1

由于平面 class 是用 "init(_ anchor: ARPlaneAnchor)" 初始化的，即使它被声明为 SCNNode class 它 returns 与块 2 中的纯 SCNNode 不同的实例.

我不是变异主题的专家，但认为 Apple 博客中有一份有趣的文档 The Role of Mutation in Safety

不太确定，但由于 class 本质上是可变的，您可能可以将更新功能移动到平面 class 作为（测试）解决方案

Answer 2

Inout 不适用于 `Subclass`

这是例子

class SuperClass {
    var name = "Prashant"

}

class TestObject:SuperClass {
}


func updateTemp ( object:inout SuperClass) {
    object.name = "P.T"
}

现在，当您创建 TestObject 对象时，它是 SuperClass 的子class 对象，它将不允许这样做。

var obj  = TestObject()
self.updateTemp(object: &obj) // Cannot pass immutable value as inout argument: implicit conversion from 'TestObject' to 'SuperClass' requires a temporary
print(obj.name)

如何解决这个问题

三种方式

1) 使用 var obj:SuperClass = TestObject()

创建对象

2) 这实际上不需要是 inout 因为 class 是引用类型

3) 像这样创建泛型函数（泛型很棒！！）

func updateTemp<T:SuperClass> ( object:inout T) {
    object.name = "P.T"
}

希望对大家有帮助

Inout 不使用 SubClass 对象抛出无法将不可变值作为 inout 参数传递

Inout not working with SubClass object throws Cannot pass immutable value as inout argument

swift

arkit

inout

Inout 不适用于 `Subclass`

如何解决这个问题

Inout 不使用 SubClass 对象抛出无法将不可变值作为 inout 参数传递

Inout not working with SubClass object throws Cannot pass immutable value as inout argument

swift

arkit

inout

Inout 不适用于 Subclass

如何解决这个问题

Inout 不适用于 `Subclass`