A Swift Journey

The story (so far) of how the mobile team at 3Squared moved to 100% Swift development for all new iOS projects. Topics covered include:

• What different approaches were taken to learning Swift.

• How the right projects were identified for 100% Swift development from the start.

• A tour of the reusable code components developed by the team which are now used in all new apps.

• The plan for the future - how to get off Objective-C for good!

Transcript

1. A Swift Journey
   Luke Stringer
   

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2. Hi, I'm Luke !
   @lukestringer90
   

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3. I'm the Head of
   Mobile 3Squared
   • Software for Rail and Construction
   industries
   • Based in Sheffield
   • Build Web apps
   • C# .NET
   • Build native iOS and Android apps
   • Swift, Objective-C & Java
   • I lead team of 7 mobile developers
   

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4. Our "Swift" Journey
   for 2 reasons...
   

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5. 1. We moved from
   Objective-C to Swift
   

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6. 2. We did it Quickly
   

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7. Our 2016 Goals
   1. Train the mobile team in Swift
   2. Move from Obj-C to Swift for new projects
   3. Develop reusable Swift code
   4. Modernise & standardise our tools and practises
   

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8. 1. Training
   

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9. Looking for Training
   We needed training materials that could be used for:
   • New / Inexperiences developers - placement students
   • Experienced non-iOS developers - Android developers
   • Experienced iOS developers
   

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10. Styles of Learning
    • Follow guided tutorials
    • Build a simple project in Swift
    • Request data from GitHub API
    • Parse & persist
    • Display on screen
    • Build a wrapper and other reusable code
    

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11. Just Do It!
    Learn whilst Building
    Something Real
    

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12. Learning & Discussion
    as a Team was Crucial
    

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13. 2. New Projects in
    Swift
    

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14. First Project
    100% Swift from the Start!
    

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15. First Project
    • Chose a small / medium complexity project
    • Evaluated Swift's readiness for production
    • Discussed code design and style as a team
    • Identified gaps in our knowledge & our tools
    

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16. Results
    • Project delivered on time
    • No major problems - Swift is production ready
    • Beginnings of an agreed code style
    • Built helpers for using Core Data & Storyboards
    

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17. The Next Projects
    Following Code Style, using
    Helpers
    

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18. Next Projets
    • 2 new projects 100% Swift from start
    • More ambitions in scope and longer in duration
    • More of the team involved
    • Followed code style
    • Used helper code from first project
    

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19. Trialling Reusable Code
    • At this stage reusable code was unversioned
    • Just dropped straight into an Xcode project
    • Provided freedom to adapt and change
    • However this led to code divergence
    • At a suitable point team decided to standardise the
    approaches
    

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20. Results
    • Both projects delivered on time
    • Code style adapted
    • Filled more gaps - Networking, Threading, Error Handling
    • Helper code adapted and now versioned using cocoapods
    

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21. 3. Reusable Code
    

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22. The "THR"
    Micro Frameworks
    (Inspired by other works)
    

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29. THRResult
    • Models success and failure
    • Extends the familiar Result type to work with do-catch error
    handling
    • Powerful, flexible and expressive
    • Credit to
    • https://github.com/antitypical/Result
    • Olivier Halligon "Asynchronous error handling"
    

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30. enum Result {
    case success(T)
    case failure(Error)
    }
    

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31. enum Result {
    case success(T)
    case failure(Error)
    }
    // Using a switch:
    switch result {
    case .success(let value):
    // process success value
    case .failure(let error):
    // handle failure error
    }
    

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32. enum Result {
    case success(T)
    case failure(Error)
    init(_ throwingExpr: () throws -> T) {
    do {
    let value = try throwingExpr()
    self = .success(value)
    } catch {
    self = .failure(error)
    }
    }
    func resolve() throws -> T {
    switch self {
    case .success(let value): return value
    case .failure(let error): throw error
    }
    }
    }
    

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33. let successResult = Result { return value }
    let failureResult = Result { throw ImportError.invalidData }
    

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34. let successResult = Result { return value }
    let failureResult = Result { throw ImportError.invalidData }
    // Using do-catch:
    do {
    let value = try result.resolve()
    // Process value
    }
    catch {
    // Handle error
    }
    

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35. let successResult = Result { return value }
    let failureResult = Result { throw ImportError.invalidData }
    // Using if let
    if let value = try? result.resolve() {
    // Process value
    }
    // or
    let value = try! result.resolve()
    

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36. THROperations
    • Preferred method for threading
    • Helpful subclasses of Operation
    • Expressive syntax for combining operations
    • Uses THRResult to report success and failure
    • Credit to
    • https://github.com/ProcedureKit/ProcedureKit
    

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37. protocol ProducesResult: class {
    associatedtype Output
    var output: Result { get set }
    }
    

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38. extension ProducesResult where Self: Operation {
    func addResultBlock(block: @escaping (Result) -> Void) {
    if let existing = completionBlock {
    completionBlock = {
    existing()
    block(self.output)
    }
    }
    else {
    completionBlock = {
    block(self.output)
    }
    }
    }
    }
    

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39. Example
    Let's build an operation to extract a top level domain (TLD)
    from a URL string
    typealias TopLevelDomain = String
    typealias URLString = String
    

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40. class ExtractTopLevelDomainOperation: Operation, ProducesResult {
    // ProducesResult
    var output: Result = Result {
    throw ResultError.noResult
    }
    // TopLevelDomainOperation
    let urlString: URLString
    init(urlString: URLString) {
    self.urlString = urlString
    }
    override func main() {
    super.main()
    extractTopLevelDomain(from: urlString)
    }
    // ...
    }
    

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41. // ...continued
    func extractTopLevelDomain(from urlString: URLString) {
    guard urlString.characters.count > 0 else {
    output = Result { throw TopLevelDomainError.invalidURL }
    return
    }
    let parts = urlString.components(separatedBy: ".")
    guard parts.count > 1, let topLevelDomain = parts.last else {
    output = Result { throw TopLevelDomainError.none }
    return
    }
    output = Result { return topLevelDomain }
    }
    

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42. let operation = ExtractTopLevelDomainOperation(urlString: "apple.com")
    operation.addResultBlock { result in
    switch result {
    case .success(let value):
    // process TLD
    case .failure(let error):
    switch error {
    case TopLevelDomainOperation.none:
    // handle no TLD
    case TopLevelDomainOperation.invalidURL:
    // handle invalid URL
    }
    }
    }
    operation.enqueue()
    

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43. let operation = ExtractTopLevelDomainOperation(urlString: "apple.com")
    operation.addResultBlock { result in
    do {
    let topLevelDomain = try result.resolve()
    // process TLD
    }
    catch {
    switch error {
    case TopLevelDomainOperation.none:
    // handle no TLD
    case TopLevelDomainOperation.invalidURL:
    // handle invalid URL
    }
    }
    }
    operation.enqueue()
    

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44. let operation = ExtractTopLevelDomainOperation(urlString: "apple.com")
    operation.addResultBlock { result in
    if let topLevelDomain = try? result.resolve() {
    // process TLD
    }
    }
    operation.enqueue()
    

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45. Combining Operations
    • Often the output from one operation is the input to another
    • We want to pass the Result onwards
    • Combining many simple operations can produce complex
    logic
    

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46. protocol ProducesResult: class {
    associatedtype Output
    var output: Result { get set }
    }
    protocol ConsumesResult: class {
    associatedtype Input
    var input: Result { get set }
    }
    

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47. class ExtractTopLevelDomainOperation: BaseOperation,
    ProducesResult,
    ConsumesResult {
    // ProducesResult
    var output: Result = Result {
    throw ResultError.noResult
    }
    // ConsumesResult
    var input: Result = Result {
    throw ResultError.noResult
    }
    // ...
    }
    

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48. // ...continued
    override func main() {
    super.main()
    do {
    let urlString = try input.resolve()
    extractTopLevelDomain(from: urlString)
    }
    catch {
    output = Result { throw error }
    }
    }
    

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49. // Output: URLString
    let getURLString = RequestURLStringOperation()
    // Input: URLString, Output: TopLevelDomain
    let extractTLD = ExtractTopLevelDomainOperation()
    // Input: TopLevelDomain, Output: Bool
    let validate = ValidateTopLevelDomainOperation()
    validate.addResultBlock { result in
    if let isValid = try? result.resolve(), isValid == true {
    // TLD is valid
    }
    }
    getURLString
    .passesResult(to: extractTLD)
    .passesResult(to: validate)
    .enqueue()
    

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51. 4. Modernise &
    Standardise
    

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52. Modernise & Standardise
    • Handle errors and unhappy paths (THRResult)
    • Perform work asynchronously (THROperations)
    • Build complex logic from smaller units (THROperations)
    • Request data over a network, then parse into core data
    (THRNetwork & THRCoreData)
    • Use storyboard segues with type safety (THRUtilities)
    • Parse dates to and from a web API (THRDate)
    

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53. Did We Meet Our
    Goals?
    

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54. Our 2016 Goals
    1. Train the mobile team in Swift
    2. Move from Obj-C to Swift for new projects
    3. Develop reusable Swift code
    4. Modernise & standardise our tools and practises
    

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55. Our 2016 Goals
    1. Train the mobile team in Swift ✅
    2. Move from Obj-C to Swift for new projects
    3. Develop reusable Swift code
    4. Modernise & standardise our tools and practises
    

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56. Our 2016 Goals
    1. Train the mobile team in Swift ✅
    2. Move from Obj-C to Swift for new projects ✅
    3. Develop reusable Swift code
    4. Modernise & standardise our tools and practises
    

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57. Our 2016 Goals
    1. Train the mobile team in Swift ✅
    2. Move from Obj-C to Swift for new projects ✅
    3. Develop reusable Swift code ✅
    4. Modernise & standardise our tools and practises
    

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58. Our 2016 Goals
    1. Train the mobile team in Swift ✅
    2. Move from Obj-C to Swift for new projects ✅
    3. Develop reusable Swift code ✅
    4. Modernise & standardise our tools and practises ✅
    

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59. Recommendations
    

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60. 1. Learn as a Team
    

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61. 2. Gain Support from
    Business
    Management
    

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62. 3. Make Space for
    Experimentation
    

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63. 4. Expect to make
    Mistakes
    

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64. Our Plan for The
    Future
    

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65. How do we stop
    writing Objective-C in
    existing apps?
    

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66. Every line of
    Objective-C written
    now is Technical Debt
    

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67. Swift alongside Objective-C
    • Understand the limitations of Obj-C/Swift interoperability
    • No structs
    • No associated values with enums
    • No protocol extensions
    • Identify new features that can be written in Swift without too
    much difficulty
    

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68. Swift alongside Objective-C
    • Replace existing standalone Obj-C classes, methods etc
    with Swift implementation
    • NSPredicate generation
    • Simple / isolated UIViewControllers
    • Replace existing Obj-C structures with THR frameworks
    • e.g. rewrite data synchronisation subsystem
    

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69. A Swift Journey
    Luke Stringer
    

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70. Any Questions? !
    

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71. References
    • http://alisoftware.github.io/swift/async/error/2016/02/06/
    async-errors/
    • https://github.com/antitypical/Result
    • https://github.com/ProcedureKit/ProcedureKit
    

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