Extension Computed Property Behavior

extension-computed-property.swift

// To maintain state of extension computed property, use static variable

// A console logger

protocol ConsoleLoggable {
	var logger: ConsoleLoggerProtocol { get }
}

extension ConsoleLoggable {
	var logger: ConsoleLoggerProtocol {
		print("New instance...")
		return DefaultConsoleLogger()
	}
}

protocol ConsoleLoggerProtocol {
	func log()
}

struct DefaultConsoleLogger: ConsoleLoggerProtocol {
	func log() {
		print("CONSOLE log...")
	}
}

// A file logger

protocol FileLoggable {
	var logger: FileLoggerProtocol { get }
}

extension FileLoggable {
	var logger: FileLoggerProtocol {
		return DefaultFileLogger()
	}
}

protocol FileLoggerProtocol {
	func log()
}

struct DefaultFileLogger: FileLoggerProtocol {
	func log() {
		print("FILE log...")
	}
}

// Test

struct LoggerTest: ConsoleLoggable {
//struct LoggerTest: FileLoggable, ConsoleLoggable {
	func test() {
		logger.log()
		logger.log()
		//clogger.log()
		//flogger.log()
	}
}

LoggerTest().test()

/**
 New instance...
 CONSOLE log...
 New instance...
 CONSOLE log...
*/