A generic builder that allows me to inject dependencies into the built objects

PricelessGenericBuilder.swift

  
// With gratitude to David Harris http://davidharris.io/
// for his article on making generic factories. I might keep some of my hair.
//
// http://davidharris.io/ios/swift/2018/03/19/generic-factory.html

import Foundation

open class Builder<DependencyType> {
    public typealias DependencyCreator = () -> DependencyType
    public var dependencyCreator: DependencyCreator?
    
    public func inject(dependencyCreator: @escaping DependencyCreator) {
        self.dependencyCreator = dependencyCreator
    }
    
    public func create() -> DependencyType? {
        if let d = dependencyCreator { return d() }
        else { print("no creator") ; return nil }
    }
}

typealias NodeStatusCallback = (_ b: Bool) -> ()

protocol SplicerNode: class {
//    var nodeCounter: NodeCounter? { get set }
//    func showMessage(_ message: String)
}

class FakeSplicerNode: SplicerNode {
    var nodeCounter = NodeCounter()

    init(nodeCounter: NodeCounter) {
        self.nodeCounter = nodeCounter
        nodeCounter.count += 1
    }
    
    deinit { nodeCounter.count -= 1 }

    func showMessage(_ message: String) { print(message) }
}

class RealSplicerNode: SplicerNode {
    var nodeCounter = NodeCounter()
    
    init(nodeCounter: NodeCounter) {
        self.nodeCounter = nodeCounter
        nodeCounter.count += 1
    }
    
    deinit { nodeCounter.count -= 1 }

    func showMessage(_ message: String) { print(message) }
}

class NodeCounter {
    var count = 0
}

class Splicer<T: SplicerNode> { }
class FakeSplicer: Splicer<FakeSplicerNode> {  }
class RealSplicer: Splicer<RealSplicerNode> { }

class FakeNodeBuilder: Builder<FakeSplicerNode> {
    var nodeCounter = NodeCounter()
    
    override init() {
        super.init()
        self.inject { FakeSplicerNode(nodeCounter: self.nodeCounter) }
    }
    
    func nodeStatusCallback(_ alive: Bool) {
        print("Fake", alive, nodeCounter.count)
    }
}

class RealNodeBuilder: Builder<RealSplicerNode> {
    var nodeCounter = NodeCounter()

    override init() {
        super.init()

        self.inject { RealSplicerNode(nodeCounter: self.nodeCounter) }
    }

    func nodeStatusCallback(_ alive: Bool) {
        print("Fake", alive, nodeCounter.count)
    }
}

let fakeSplicer = FakeSplicer()
let realSplicer = RealSplicer()

let fakeNodeBuilder = FakeNodeBuilder()
let realNodeBuilder = RealNodeBuilder()

let fakeNode = fakeNodeBuilder.create()
let realNode = realNodeBuilder.create()

print("Fake node count = \(fakeNodeBuilder.nodeCounter.count)")
print("Real node count = \(realNodeBuilder.nodeCounter.count)")

let fakeNode2 = fakeNodeBuilder.create()
let realNode2 = realNodeBuilder.create()

print("Fake node count = \(fakeNodeBuilder.nodeCounter.count)")
print("Real node count = \(realNodeBuilder.nodeCounter.count)")