Swift Playground Drawing

Here are 3 custom UIViews that I have built in order to learn how to draw three simple elements: a circle, a square and a line in Swift 4.
In order to keep everything simple, the border color is UIColor.black.cgColor and the fill color is UIColor.darkGray.cgColor.

Line

The SimpleLine class lets you specify the starting point and the ending point of a line.

let firstLine = SimpleLine(from: CGPoint(x: 60, y: 40), to: CGPoint(x: 300, y: 300))

Square

The SimpleRectangle class lets you specify the top left corner of the square you are drawing and its size.

let firstRectangle = SimpleRectangle(topLeftCorner: CGPoint(x: 120, y:100), size: 80)

Circle

The SimpleCircle class lets you specify the top left corner of the square where the circle is placed, and the size of the circle.

let firstCircle = SimpleCircle(topLeftCorner: CGPoint(x: 80, y: 80), size: 80)