Example of the builder pattern in Swift with protocols

builder-pattern.swift

//Playground friendly

import Foundation
/*
 The Builder Pattern helps in the creation of complex objects
 
 *Implemented with Protocols
 */

/* Before Builder Pattern is implemented */
struct ComplexType {
    var id: Int
    var name: String
    var usage: String
    var date: NSDate
    var line1: String
    var line2: String
    var line3: String
    var value1: Int
    var value2: Int
    var value3: Double
}

/* Feels clumsy and prone to error */
let exampleObject1 = ComplexType(id: 1, name: "Example Object 1", usage: "No pattern example",
                                  date: NSDate(), line1: "", line2: "",
                                  line3: "", value1: 1, value2: 2, value3: 3.00)

/* 
 With Builder Pattern 
 */

//Implement protocol with all parameters needed for constructor
protocol ComplexTypeBuilder {
    var id: Int { get }
    var name: String { get }
    var usage: String { get }
    var date: NSDate { get }
    var line1: String { get }
    var line2: String { get }
    var line3: String { get }
    var value1: Int { get }
    var value2: Int { get }
    var value3: Double { get }
}

//Implement structs that have the logic for setting these values
struct ExampleComplexType1: ComplexTypeBuilder {
    let id: Int
    let name = "Example Object 1"
    let usage = "Showcase Builder pattern"
    let date = NSDate()
    let line1 = ""
    let line2 = ""
    let line3 = ""
    let value1 = 1
    let value2 = 2
    let value3 = 3.0
    
    init(id: Int) {
        self.id = id
    }
}

struct ExampleComplexType2: ComplexTypeBuilder {
    let id: Int
    let name = "Example Object 2"
    let usage = "Reinforce Builder pattern"
    let date = NSDate()
    let line1 = ""
    let line2 = ""
    let line3 = ""
    let value1 = 3
    let value2 = 2
    let value3 = 1.0
    
    init(id: Int) {
        self.id = id
    }
}

//Refactored complex type can now accept one arguement of a ComplexBuilderType type
struct BuilderBasedComplexType {
    var id: Int
    var name: String
    var usage: String
    var date: NSDate
    var line1: String
    var line2: String
    var line3: String
    var value1: Int
    var value2: Int
    var value3: Double
    
    init(builder: ComplexTypeBuilder) {
        self.id = builder.id
        self.name = builder.name
        self.usage = builder.usage
        self.date = builder.date
        self.line1 = builder.line1
        self.line2 = builder.line2
        self.line3 = builder.line3
        self.value1 = builder.value1
        self.value2 = builder.value2
        self.value3 = builder.value3
    }
}

/* Initialization is now more succint */
let builderBasedComplexType = BuilderBasedComplexType(builder: ExampleComplexType1(id: 1))
assert(builderBasedComplexType.id == 1)