Swift 5's Custom String Interpolation in Practice

Transcript

1. Using Swift 5's
   Custom String
   Interpolation in
   Practice
   @basthomas, Copenhagen Cocoa, 06-02-2020 1
   

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2. Who am I
   • Swift Weekly Brief
   • Contravariance (stickers)
   • RayWenderlich tech editor
   • iOS Platform at XING
   @basthomas, Copenhagen Cocoa, 06-02-2020 2
   

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3. Where do we come
   from?
   @basthomas, Copenhagen Cocoa, 06-02-2020 3
   

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4. !
   @basthomas, Copenhagen Cocoa, 06-02-2020 4
   

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5. NSString *name = @"Bas";
   [NSString stringWithFormat:@"Hello, %@", name];
   [NSString stringWithFormat:@"%.2f", 9.0234];
   [NSString stringWithFormat:
   @"Hello %@, how are you doing this %@? %@",
   @"Bas",
   @"evening",
   @"Great!"
   ];
   @basthomas, Copenhagen Cocoa, 06-02-2020 5
   

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6. ✨
   @basthomas, Copenhagen Cocoa, 06-02-2020 6
   

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7. let name = "Bas"
   "Hello, \(name)"
   String(format: "%.2f", 9.0234) //
   "Hello \(name), how are you doing this \(timeOfDay)?"
   @basthomas, Copenhagen Cocoa, 06-02-2020 7
   

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8. It is very good.
   @basthomas, Copenhagen Cocoa, 06-02-2020 8
   

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9. Interlude
   @basthomas, Copenhagen Cocoa, 06-02-2020 9
   

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10. Swift Evolution
    @basthomas, Copenhagen Cocoa, 06-02-2020 10
    

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11. Multiline String Literals (SE-0168)
    """
    Hello,
    how are you doing
    this \(timeOfDay)?
    """
    @basthomas, Copenhagen Cocoa, 06-02-2020 11
    

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12. String Literal Delimiters (SE-0200)
    // before
    "\"Did you put your name into the Goblet of Fire, Harry?\" he asked calmly."
    // after
    #""Harry! Did you put your name in the Goblet of Fire?!""#
    @basthomas, Copenhagen Cocoa, 06-02-2020 12
    

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13. And then...
    @basthomas, Copenhagen Cocoa, 06-02-2020 13
    

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14. Custom String
    Interpolation
    (aka Fix ExpressibleByStringInterpolation)
    @basthomas, Copenhagen Cocoa, 06-02-2020 14
    

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15. Localization
    @basthomas, Copenhagen Cocoa, 06-02-2020 15
    

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16. let message: LocalizableString =
    #"The document "\(name)" could not be saved."#
    alert.messageText = String(localized: message)
    @basthomas, Copenhagen Cocoa, 06-02-2020 16
    

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17. Errors
    @basthomas, Copenhagen Cocoa, 06-02-2020 17
    

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18. extension String.StringInterpolation {
    mutating func appendInterpolation(_ error: Error) {
    appendLiteral(error.localizedDescription)
    }
    }
    fatalError(
    "Something went wrong: \(ConnectionError.invalidRequest)"
    )
    @basthomas, Copenhagen Cocoa, 06-02-2020 18
    

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19. Number formatting
    @basthomas, Copenhagen Cocoa, 06-02-2020 19
    

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20. extension String.StringInterpolation {
    mutating func appendInterpolation(
    number: Double,
    formatter: NumberFormatter
    ) {
    appendInterpolation(
    ifNotNil: formatter.string(from: NSNumber(value: number))
    )
    }
    }
    let priceFormatter = NumberFormatter()
    priceFormatter.numberStyle = .currency
    "\(number: 100.1234, formatter: priceFormatter)"
    @basthomas, Copenhagen Cocoa, 06-02-2020 20
    

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21. Logging and privacy
    @basthomas, Copenhagen Cocoa, 06-02-2020 21
    

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22. extension String.StringInterpolation {
    mutating func appendInterpolation(private: String) {
    #if DEBUG
    appendLiteral(`private`)
    #else
    appendLiteral("@@@")
    #endif
    }
    }
    let name = "Bas"
    let password = "Broek"
    print("User \(name) has password \(private: password)")
    @basthomas, Copenhagen Cocoa, 06-02-2020 22
    

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23. Other instances
    @basthomas, Copenhagen Cocoa, 06-02-2020 23
    

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24. "\(properties == nil ? "nil" : String(describing: properties ?? [:]))"
    @basthomas, Copenhagen Cocoa, 06-02-2020 24
    

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25. extension String.StringInterpolation {
    mutating func appendInterpolation(
    dictionary: Dictionary?,
    default: @autoclosure () -> String = "nil"
    ) {
    if let dictionary = dictionary {
    appendLiteral(String(describing: dictionary))
    } else {
    appendLiteral(`default`())
    }
    }
    }
    "\(dictionary: properties)"
    @basthomas, Copenhagen Cocoa, 06-02-2020 25
    

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26. 123 > maxBadgeCount ? String("\(maxBadgeCount)+") : String(123)
    @basthomas, Copenhagen Cocoa, 06-02-2020 26
    

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27. extension String.StringInterpolation {
    mutating func appendInterpolation(
    number: Int,
    maximum: @autoclosure () -> Int
    ) {
    let max = maximum()
    if number > max {
    appendLiteral("\(max)+")
    } else {
    appendLiteral("\(number)")
    }
    }
    }
    "\(number: number, maximum: maxBadgeCount)"
    @basthomas, Copenhagen Cocoa, 06-02-2020 27
    

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28. !
    @basthomas, Copenhagen Cocoa, 06-02-2020 28
    

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29. Polluting a
    namespace
    @basthomas, Copenhagen Cocoa, 06-02-2020 29
    

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30. Code, documentation,
    tests
    @basthomas, Copenhagen Cocoa, 06-02-2020 30
    

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31. struct BadgeCount: CustomStringConvertible {
    let value: Int
    var maximum = 99
    var description: String {
    if value > maximum {
    return "\(maximum)+"
    } else {
    return "\(value)"
    }
    }
    }
    "\(BadgeCount(value: 123, maximum: 99))"
    "\(BadgeCount(value: 123))"
    @basthomas, Copenhagen Cocoa, 06-02-2020 31
    

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32. Going all in
    @basthomas, Copenhagen Cocoa, 06-02-2020 32
    

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33. struct HTMLComponent: ExpressibleByStringLiteral, ExpressibleByStringInterpolation, CustomStringConvertible {
    struct StringInterpolation: StringInterpolationProtocol {
    var output = ""
    init(literalCapacity: Int, interpolationCount: Int) {
    output.reserveCapacity(literalCapacity * 2)
    }
    mutating func appendLiteral(_ literal: String) {
    output.append(literal)
    }
    mutating func appendInterpolation(twitter: String) {
    output.append("@\(twitter)")
    }
    mutating func appendInterpolation(email: String) {
    output.append("\(email)")
    }
    }
    let description: String
    init(stringLiteral value: String) {
    description = "\(value)"
    }
    init(stringInterpolation: StringInterpolation) {
    self.init(stringLiteral: stringInterpolation.output)
    }
    }
    @basthomas, Copenhagen Cocoa, 06-02-2020 33
    

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34. struct StringInterpolation: StringInterpolationProtocol {
    var output = ""
    init(literalCapacity: Int, interpolationCount: Int) {
    output.reserveCapacity(literalCapacity * 2)
    }
    mutating func appendLiteral(_ literal: String) {
    output.append(literal)
    }
    mutating func appendInterpolation(twitter: String) {
    output.append("@\(twitter)")
    }
    mutating func appendInterpolation(email: String) {
    output.append("\(email)")
    }
    }
    let html: HTMLComponent = "Find me on \(twitter: "basthomas") or send an email to \(email: "bas@basbroek.nl")"
    // Find me on @basthomas
    // or send an email to bas@basbroek.nl
    @basthomas, Copenhagen Cocoa, 06-02-2020 34
    

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35. Optimize code for
    reading, not writing
    @basthomas, Copenhagen Cocoa, 06-02-2020 35
    

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36. Communication is
    hard
    @basthomas, Copenhagen Cocoa, 06-02-2020 36
    

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37. Thanks!
    @basthomas
    @basthomas, Copenhagen Cocoa, 06-02-2020 37
    

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