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
   

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2. Protocols
   Are Not New
   To Cocoa
   

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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
   

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5. struct Homer {
   ...
   var krusty: Krusty
   }
   Not much good having an embedded Krusty object.
   

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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?
   

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7. We could declare an array of Franchisees
   let franchisees: Array = [“Homer”, “Ned”, “Smithers”]
   But then we have to declare a delegate object for
   each. of them, or use some kind of factory method.
   

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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
   

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9. So for something like this:
   [1, 2, 3, 5, 10, 15]
   We get:
   [“1”, “2”, “Buzz”, “Fizz”, “Fizz”, “FizzBuzz”]
   

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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)”
    }
    }
    }
    }
    

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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
    }
    }
    }
    

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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
    }
    }
    }
    

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13. Create a FizzBuzz Protocol
    protocol FizzBuzzable {
    func fizzBuzzValue() -> Int
    }
    

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14. Create a FizzBuzz Protocol
    protocol FizzBuzzable {
    func fizzBuzzValue() -> Int
    }
    extension Int: FizzBuzzable {
    func fizzBuzzValue() -> Int {
    return self
    }
    }
    

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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
    }
    }
    }
    

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16. This works
    [1, 3, 5, 10, 15].fizzBuzz( [(3, “Fizz”), (5, “Buzz”)] )
    // [“1”, “Fizz”, “Buzz”, “Buzz”, “FizzBuzz”]
    

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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
    }
    }
    

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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.
    

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20. data TrafficLight = Red | Yellow | Green deriving (Eq, Ord, Show)
    let r = Red
    let g = Green
    r == g # False
    r < g # True
    r # Red
    

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23. https://realm.io/news/altconf-
    airspeed-velocity-bottom-up-
    programming-in-swift/
    

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24. This is what it’s like to
    read a blog post.
    

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25. This is what we have to do
    to properly internalise new
    stuff.
    

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26. Thank You
    Abizer Nasir | @abizern | abizern.org
    

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