DSLs in Swift

A talk I given at SwiftCrunch http://swiftcrunch.com, the first ever hack day on Swift.

https://github.com/kylef/QueryKit
https://twitter.com/kylefuller

Transcript

1. DESIGNING | BUILDING
   DSLS IN SWIFT
   @KYLEFULLER
   

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4. BASE
   

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6. SHAPE
   

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7. WHAT IS A DSL?
   

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8. DOMAIN SPECIFIC
   LANGUAGE
   

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9. PROGRAMMING
   LANGUAGE
   

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10. DECLARATIVE
    

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12. SPECIFIC
    

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13. NOT GENERIC
    

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14. FREEDOM
    

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15. BUGS
    

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16. NSPredicate
    

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17. NAME EQUALS Kyle
    

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18. USING
    NSPredicate
    

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19. NSExpression *left = [NSExpression expressionForKeyPath:@"name"];
    NSExpression *right = [NSExpression expressionForConstantValue:@"Kyle"];
    [NSComparisonPredicate
    predicateWithLeftExpression:left
    rightExpression:right
    modifier:NSDirectPredicateModifier
    type:NSEqualToPredicateOperatorType
    options:0];
    

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20. IMPERATIVE
    

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21. FRUSTRATING
    

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22. [NSPredicate predicateWithFormat:@"name == Kyle"];
    

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23. EASY TO WRITE
    BUGS
    

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24. [NSPredicate predicateWithFormat:@"nme == Kyle"];
    

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25. NSString *key = NSStringFromSelector(@selector(name));
    [NSPredicate predicateWithFormat:@"%K == Kyle", key];
    

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26. INELEGANT
    

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27. DSLS
    

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28. [[Person name] equals:@"Kyle"]
    

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29. SWIFT
    

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30. CUSTOM
    OPERATORS
    

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31. (Something) == (Something else)
    

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32. / = - + * % <
    > ! & | ^ . ~
    

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33. Person.name == "Kyle"
    

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34. IDEA
    

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35. CORE DATA
    DSL
    

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36. MAKING A QUERY IN
    CORE DATA
    

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37. let fetchRequest = NSFetchRequest(entityName: "Person")
    fetchRequest.predicate = NSPredicate(format:"name == %@", "Kyle")
    fetchRequest.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)]
    var error:NSErrorPointer?
    var objects = managedObjectContext.executeFetchRequest(fetchRequest, error:error!)
    if let objects = objects {
    ;
    }
    

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38. 6 LINES
    

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39. Person.queryset(context)
    .orderBy(Person.name.ascending)
    .filter(Person.name == "Kyle")
    

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40. 1 LINE
    

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41. REFACTORING
    

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42. class Person : NSManagedObject {
    var name:String?
    - var age:NSNumber?
    }
    

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43. class Person : NSManagedObject {
    var name:String?
    - var age:NSNumber?
    + var birthday:NSDate?
    }
    

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44. BUILD
    SUCCESSFUL
    

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46. *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath age not found in entity '
    *** First throw call stack:
    (
    0 CoreFoundation 0x00000001039e5495 __exceptionPreprocess + 165
    1 libobjc.A.dylib 0x0000000102fe199e objc_exception_throw + 43
    2 CoreData 0x0000000100b04438 -[NSSQLGenerator newSQLStatementForFetchRequest:ignoreInheritance:countOnly:nestingLevel:] + 904
    3 CoreData 0x0000000100b03f6d -[NSSQLAdapter _newSelectStatementWithFetchRequest:ignoreInheritance:] + 365
    4 CoreData 0x0000000100b03bd3 -[NSSQLCore newRowsForFetchPlan:] + 115
    5 CoreData 0x0000000100b034a4 -[NSSQLCore objectsForFetchRequest:inContext:] + 516
    6 CoreData 0x0000000100b03025 -[NSSQLCore executeRequest:withContext:error:] + 245
    7 CoreData 0x0000000100b02b60 -[NSPersistentStoreCoordinator executeRequest:withContext:error:] + 3504
    8 CoreData 0x0000000100b00a21 -[NSManagedObjectContext executeFetchRequest:error:] + 497
    9 Fitness First 0x000000010021d89a -[KFObjectManager array:] + 138
    10 Fitness First 0x00000001000c6396 -[FFGDashboardViewController viewWillAppear:] + 1190
    11 UIKit 0x0000000101ae8db5 -[UIViewController _setViewAppearState:isAnimating:] + 422
    12 UIKit 0x0000000101d42410 -[UIWindowController transition:fromViewController:toViewController:target:didEndSelector:animation:] + 5629
    13 UIKit 0x0000000101aeffce -[UIViewController presentViewController:withTransition:completion:] + 4854
    )
    libc++abi.dylib: terminating with uncaught exception of type NSException
    

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47. Keypath age not found in entity
    
    

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48. class Person : NSManagedObject {
    var name:String?
    - var age:NSNumber?
    + var birthday:NSDate?
    }
    

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49. NSSortDescriptor(key: "age", ascending: true)
    

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50. COULD WE DO THIS
    BETTER
    WITH A DSL?
    

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51. SAY NO TO HARD
    CODED STRINGS
    

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52. Person.age.ascending
    

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53. READABILITY
    

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54. SAFE
    

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56. DSLS ARE
    !
    

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57. !
    

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58. DON'T ABUSE THE POWER
    Swift HAS GIVEN US.
    

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59. GOING TOO FAR
    

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60. BAD
    

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61. Person.name %= "Kyle"
    

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62. CONSIDERATION
    

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63. INTUITIVE
    

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64. >>> Person.age > 27
    Age is more than 27
    

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65. >>> Person.name %= "Kyle"
    Name is ? Kyle
    

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66. >>> Person.name ~= "Kyle"
    Name is LIKE Kyle
    

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67. WHERE TO
    START?
    

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68. README
    

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70. README
    

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71. PLAYGROUNDS
    

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72. QuerySet().filter(Person.name == "Kyle")
    .orderBy(Person.name.ascending)
    

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74. class Attribute {
    var ascending:NSSortDescriptor {
    return NSSortDescriptor(key: "x", ascending: true)
    }
    var descending:NSSortDescriptor {
    return NSSortDescriptor(key: "x", ascending: true)
    }
    }
    @infix func == (left: Attribute, right: AnyObject) -> NSPredicate {
    return NSPredicate(format: "x", nil)
    }
    

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75. class QuerySet {
    func orderBy(sortDescriptor:NSSortDescriptor) -> QuerySet {
    return self
    }
    func filter(predicate:NSPredicate) -> QuerySet {
    return self
    }
    subscript(range: Range) -> QuerySet {
    return self
    }
    }
    

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76. class Person {
    class var name:Attribute {
    return Attribute()
    }
    }
    QuerySet().filter(Person.name == "Kyle")
    .orderBy(Person.name.ascending)
    

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77. !
    

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78. WHAT'S NEXT?
    

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79. WRITING THE
    REAL
    IMPLEMENTATION
    

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86. 04:00 AM
    

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91. github.com/kylef/QueryKit
    

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92. twitter.com/kylefuller
    

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94. github.com/kylef/QueryKit
    twitter.com/kylefuller
    

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