Protocol extensions is one of the beautiful features of Swift language.
Let’s see the usefulness with a use case.
I have a Logger protocol which is having simple log function which takes string to be logged and logs it.
protocol Logger {
func log(message: String)
}
I am taking 3 service classes which has to confirm to this Logger protocol for logging service errors.
class FacebookServices: Logger {
func log(message: String) {
print("Facebook - \(message)")
}
}
class TwitterServices: Logger {
func log(message: String) {
print("Twitter - \(message)")
}
}
class InstagramServices: Logger {
func log(message: String) {
print("Instagram - \(message)")
}
}
All the 3 classes are confirming to Logger protocol and implemented interface method log.
Now, What If we need log a generic error like "Service Unavailable”.
We need to write that in all the 3 classes or we need to take a base class and keep the logGenericError method there.
class FacebookServices: Logger {
func log(message: String) {
print("Facebook - \(message)")
}
func logGenericError() {
print("Service unavailable!")
}
}
class TwitterServices: Logger {
func log(message: String) {
print("Twitter - \(message)")
}
func logGenericError() {
print("Service unavailable!")
}
}
class InstagramServices: Logger {
func log(message: String) {
print("Instagram - \(message)")
}
func logGenericError() {
print("Service unavailable!")
}
}
Instead of this, We can extend the Logger protocol and keep our convenient API there which allows all the classes confirming to the portal can access that extension.
extension Logger {
func logGenericError() {
print("Service unavailable!")
}
}
let twitter = TwitterServices()
let facebook = FacebookServices()
twitter.log(message: "404")
twitter.logGenericError() // Service unavailable!
twitter.log(message: "500")
twitter.logGenericError() // Service unavailable!
Easy and very useful Right?
We can customise the logGenericError() If a service needs like shown below.
class InstagramServices: Logger {
func log(message: String) {
print("Instagram - \(message)")
}
func logGenericError() {
print("Please try later!")
}
}
let instagram = InstagramServices()
instagram.logGenericError() // Please try later!
Go with Protocol extensions in such use cases instead of going for base classes.
Hope this post is useful. Feel free to comment incase of any queries.
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