Swift游乐场:当在内置的变量查看器中显示时，花车始终是圆形的

import UIKit
import PlaygroundSupport

class CarView: UIView {
    var shape: String = "circle" {
        didSet {
            setNeedsDisplay()
        }
    }
    
    override func draw(_ rect: CGRect) {
        let path = UIBezierPath()
        if shape == "circle" {
            path.addArc(withCenter: CGPoint(x: rect.midX, y: rect.midY), radius: min(rect.width, rect.height) / 2, startAngle: .zero, endAngle: .pi * 2, clockwise: true)
        } else if shape == "square" {
            path.move(to: CGPoint(x: rect.minX, y: rect.minY))
            path.addLine(to: CGPoint(x: rect.maxX, y: rect.minY))
            path.addLine(to: CGPoint(x: rect.maxX, y: rect.maxY))
            path.addLine(to: CGPoint(x: rect.minX, y: rect.maxY))
            path.close()
        }
        UIColor.blue.setFill()
        path.fill()
    }
}

let carView = CarView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
carView.shape = "circle" // 或者 "square"
PlaygroundPage.current.liveView = carView