static member lookup progress

gistfile1.txt

import UIKit
import PlaygroundSupport

protocol ProgressRenderer {
    var draw: (Double, CGRect) -> Void { get }
}

struct ConcreteProgressRenderer: ProgressRenderer {
    let draw: (Double, CGRect) -> Void
}

extension ProgressRenderer where Self == ConcreteProgressRenderer {
    static func arc(color: UIColor) -> ConcreteProgressRenderer {
        .init { proportion, rect in
            let radius: Double = min(rect.width, rect.height) / 2
            let center = CGPoint(x: rect.midX, y: rect.midX)
            let path = UIBezierPath()
            color.setFill()
            path.move(to: center)
            path.addLine(to: .init(x: 0, y: radius))
            path.addArc(withCenter: center, radius: radius, startAngle: 0, endAngle: proportion * 2 * .pi, clockwise: true)
            path.close()
            path.fill()
        }
    }
    static func ring(width: Double, color: UIColor) -> ConcreteProgressRenderer {
        .init { proportion, rect in
            color.setStroke()
            let center = CGPoint(x: rect.midX, y: rect.midX)
            let radius: Double = (min(rect.width, rect.height) - width) / 2
            let path = UIBezierPath(arcCenter: center, radius: radius, startAngle: 0, endAngle:  proportion * 2 * .pi, clockwise: true)
            path.lineWidth = width
            path.lineCapStyle = .round
            path.stroke()

        }
    }
}

final class ProgressView: UIView {
    var proportion = 0.0 {
        didSet {
            setNeedsDisplay()
        }
    }
    private let renderer: ProgressRenderer
    init(_ renderer: ProgressRenderer) {
        self.renderer = renderer
        super.init(frame: .zero)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func draw(_ rect: CGRect) {
        renderer.draw(proportion, rect)
    }
}

let progressView = ProgressView(.arc(color: .blue))
progressView.frame = .init(origin: .zero, size: .init(width: 200, height: 200))
progressView.transform = .init(rotationAngle: -.pi / 2)
PlaygroundPage.current.liveView = progressView

let progressSubscription = Timer
    .publish(every: 0.05, on: .main, in: .common)
    .autoconnect()
    .map { _ in 0.01 }
    .scan(0.0, +)
    .sink(receiveValue: { progressView.proportion = $0 })