And example of using a struct singleton with only static properties. The static properties are enforced with the protocol. We can still use dependency injection which means we can do away with the "sharedInstance" construct.

Struct_Singleton_3ProtocolSplit.swift

protocol Singleton3_Protocol {
	static var queue: OperationQueue { get }
	static func method1()
}

protocol Name {
	static var name: String { get set }
}

protocol Singleton3_Protocol2: Name {
	static var queue2: OperationQueue { get }
	static func method2()
}

protocol Singleton3_Protocol3: Name {
	static var queue3: OperationQueue { get }
	static func method3()
}

struct Singleton3: Singleton3_Protocol {
	static let queue = OperationQueue()
	
	static func method1() {
		print(1, " ", queue)
	}
}

struct SubclassSingleton3: Singleton3_Protocol, Singleton3_Protocol2, Singleton3_Protocol3 {
	static var name: String = ""
	static let queue = OperationQueue()
	static let queue1 = OperationQueue()
	static let queue2 = OperationQueue()
	static let queue3 = OperationQueue()
	
	static func method1() {
		print(2, " ", queue)
		print(queue1)
	}
	
	static func method2() {
		print(2, " ", queue)
		print(queue1)
	}
	
	static func method3() {
		print(3, " ", queue)
		print(queue1)
	}
}

class Weird2 {
	
	var dependency: Singleton3_Protocol.Type = Singleton3.self
	
	func bar() {
		dependency.method1()
	}
}