Swift - boundingBox导致EXC_BAD_ACCESS（代码= 1）

Question

我正在使用SceneKit来显示文本节点。这是我的代码：

// foo.swift
extension SCNNode {
    func getNodeSize() -> (width: Float, height: Float) {
        let (min, max) = boundingBox
        return (width: max.x - min.x, height: max.y - min.y)
    }

    func setPivotCenter() {
        let (min, max) = boundingBox
        let x = min.x + 0.5 * (max.x - min.x)
        let y = min.y + 0.5 * (max.y - min.y)
        let z = min.z + 0.5 * (max.z - min.z)
        self.pivot = SCNMatrix4MakeTranslation(x, y, z)
    }
}

// bar.swift
func foo() {
    let textGeometry = SCNText(string: "foo", extrusionDepth: 0.01)
    let textNode = SCNNode(geometry: textGeometry)

    // set pivot
    textNode.setPivotCenter()

    // get size
    let (width, height) = textNode.getNodeSize()

    // some other codes
}

但是有时（偶然性）在getNodeSize（）函数中崩溃了：

symbol stub for: (extension in SceneKit):__C.SCNBoundingVolume.boundingBox.getter : (min: __C.SCNVector3, max: __C.SCNVector3)

EXC_BAD_ACCESS (code=1, address=0xxx)

or

malloc: *** error for object 0x283811360: pointer being freed was not allocated

我将两个扩展功能代码更改为一个，然后一切似乎都正常：

// bar.swift
func foo() {
    let textGeometry = SCNText(string: "foo", extrusionDepth: 0.01)
    let textNode = SCNNode(geometry: textGeometry)
    let (min, max) = textNode.boundingBox

    // set pivot
    let x = min.x + 0.5 * (max.x - min.x)
    let y = min.y + 0.5 * (max.y - min.y)
    let z = min.z + 0.5 * (max.z - min.z)
    textNode.pivot = SCNMatrix4MakeTranslation(dx, dy, dz)

    // get size
    let (width, height) = (width: max.x - min.x, height: max.y - min.y)

    // some other codes
}

我的环境：

macOS：10.14 Beta（18A293u）

Xcode：10.0 beta（10L176w）

斯威夫特：4.2

提前谢谢大家。