Protocols. What's the Big Deal?

Slides from my Swift London Talk about Protocols in Swift

Transcript

1. Protocols: What’s the Big Deal? Abizer Nasir | @abizern | abizern.org
2. Protocols Are Not New To Cocoa
3. - I conform to a protocol, so I honour this interface - Apply a common set of behaviours in a single inheritance system. UITableViewDataSource UIApplicationDelegate NSFetchedResultsSectionInfo
5. struct Homer { ... var krusty: Krusty } Not much good having an embedded Krusty object.
6. struct Homer { ... var krusty: KrustyDelegate } Whenever we want to do something Krusty like - we bounce out to the delegate But what about the other Franchisees?
7. We could declare an array of Franchisees let franchisees: Array<T: KrustyDelegate> = [“Homer”, “Ned”, “Smithers”] But then we have to declare a delegate object for each. of them, or use some kind of factory method.
8. FizzBuzz — If the number is a multiple of 3, print “Fizz” — If the number is a multiple of 5, print “Buzz” — If the number is a multiple of 3 and 5, print “FizzBuzz” — Otherwise, just print the number
9. So for something like this: [1, 2, 3, 5, 10, 15] We get: [“1”, “2”, “Buzz”, “Fizz”, “Fizz”, “FizzBuzz”]
10. Extend Protocol to deal with this extension SequenceType where Generator.Element == Int { func fizzBuzz() -> [String] { return self.map { item -> String in switch (item % 3, item % 5) { case (0, 0): return “FizzBuzz” case (0, _): return “Buzz” case (_, 0): return “Fizz” default: return “\(item)” } } } }
11. Provide configuration extension SequenceType where Generator.Element == Int { func fizzBuzz(options: [(Int, String)]) -> [String] { return self.map { item -> String in var output = “” for (divisor, description) in options { if item % divisor == 0 { output += description } } guard !output.isEmpty else { return “\(item)” } return output } } }
12. Add a type constraint extension SequenceType where Generator.Element == Int, Generator.Element: CustomStringConvertible { func fizzBuzz(options: [(Int, String)]) -> [String] { return self.map { item -> String in var output = “” for (divisor, description) in options { if item % divisor == 0 { output += description } } guard !output.isEmpty else { return item.description } return output } } }
13. Create a FizzBuzz Protocol protocol FizzBuzzable { func fizzBuzzValue() -> Int }
14. Create a FizzBuzz Protocol protocol FizzBuzzable { func fizzBuzzValue() -> Int } extension Int: FizzBuzzable { func fizzBuzzValue() -> Int { return self } }
15. Change the Type Constraint extension SequenceType where Generator.Element: FizzBuzzable, Generator.Element: CustomStringConvertible { func fizzBuzz(options: [(Int, String)]) -> [String] { return self.map { item -> String in var output = “” var value = item.fizzBuzzValue() for (divisor, description) in options { if value % divisor == 0 { output += description } } guard !output.isEmpty else { return value.description } return output } } }
16. This works [1, 3, 5, 10, 15].fizzBuzz( [(3, “Fizz”), (5, “Buzz”)] ) // [“1”, “Fizz”, “Buzz”, “Buzz”, “FizzBuzz”]
17. Extend other types to implement FizzBuzzable struct Shape { let sides: Int } extension Shape: FizzBuzzable { func fizzBuzzValue() -> Int { return sides } } extension Shape: CustomStringConvertible { var description: String { return sides.description } }
18. And you can fizz buzz that as well [Shape(sides: 1), Shape(sides: 3), Shape(sides: 15)].fizzBuzz([(3, “Fizz”), (5, “Buzz”)]) // [“1”, “Fizz”, “FizzBuzz”] The mechanics of doing the actual FizzBuzz has been removed from the configuration of the FizzBuzz.
20. data TrafficLight = Red | Yellow | Green deriving (Eq, Ord, Show) let r = Red let g = Green r == g # False r < g # True r # Red
23. https://realm.io/news/altconf- airspeed-velocity-bottom-up- programming-in-swift/
24. This is what it’s like to read a blog post.
25. This is what we have to do to properly internalise new stuff.
26. Thank You Abizer Nasir | @abizern | abizern.org