The Boxed Protocol Types example

boxed_protocol_types_example.swift

public protocol Shape {
    func draw() -> String
}

struct Triangle: Shape {
    typealias T = Int

    var size: Int
    func draw() -> String {
       var result: [String] = []
       for length in 1...size {
           result.append(String(repeating: "*", count: length))
       }
       return result.joined(separator: "\n")
    }
}

struct Square: Shape {
    typealias T = Int

    var size: Int
    func draw() -> String {
        let line = String(repeating: "*", count: size)
        let result = Array<String>(repeating: line, count: size)
        return result.joined(separator: "\n")
    }
}

struct VerticalShapes: Shape {
    var shapes: [any Shape] // boxed Shape elements by adding any before the name of a protocol
    func draw() -> String {
        return shapes.map { $0.draw() }.joined(separator: "\n\n")
    }
}


let largeTriangle = Triangle(size: 5)
let largeSquare = Square(size: 5)
let vertical = VerticalShapes(shapes: [largeTriangle, largeSquare])
print(vertical.draw())