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
4. BASE
6. SHAPE
7. WHAT IS A DSL?
8. DOMAIN SPECIFIC LANGUAGE
9. PROGRAMMING LANGUAGE
10. DECLARATIVE
12. SPECIFIC
13. NOT GENERIC
14. FREEDOM
15. BUGS
16. NSPredicate
17. NAME EQUALS Kyle
18. USING NSPredicate
19. NSExpression *left = [NSExpression expressionForKeyPath:@"name"]; NSExpression *right = [NSExpression expressionForConstantValue:@"Kyle"]; [NSComparisonPredicate predicateWithLeftExpression:left rightExpression:right modifier:NSDirectPredicateModifier type:NSEqualToPredicateOperatorType options:0];
20. IMPERATIVE
21. FRUSTRATING
22. [NSPredicate predicateWithFormat:@"name == Kyle"];
23. EASY TO WRITE BUGS
24. [NSPredicate predicateWithFormat:@"nme == Kyle"];
25. NSString *key = NSStringFromSelector(@selector(name)); [NSPredicate predicateWithFormat:@"%K == Kyle", key];
26. INELEGANT
27. DSLS
28. [[Person name] equals:@"Kyle"]
29. SWIFT
30. CUSTOM OPERATORS
31. (Something) == (Something else)
32. / = - + * % < > ! & | ^ . ~
33. Person.name == "Kyle"
34. IDEA
35. CORE DATA DSL
36. MAKING A QUERY IN CORE DATA
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 { ; }
38. 6 LINES
39. Person.queryset(context) .orderBy(Person.name.ascending) .filter(Person.name == "Kyle")
40. 1 LINE
41. REFACTORING
42. class Person : NSManagedObject { var name:String? - var age:NSNumber? }
43. class Person : NSManagedObject { var name:String? - var age:NSNumber? + var birthday:NSDate? }
44. BUILD SUCCESSFUL
46. *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'keypath age not found in entity <NSSQLEntity Person id=6>' *** 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
47. Keypath age not found in entity <NSSQLEntity Person id=6>
48. class Person : NSManagedObject { var name:String? - var age:NSNumber? + var birthday:NSDate? }
49. NSSortDescriptor(key: "age", ascending: true)
50. COULD WE DO THIS BETTER WITH A DSL?
51. SAY NO TO HARD CODED STRINGS
52. Person.age.ascending
53. READABILITY
54. SAFE
56. DSLS ARE !
57. !
58. DON'T ABUSE THE POWER Swift HAS GIVEN US.
59. GOING TOO FAR
60. BAD
61. Person.name %= "Kyle"
62. CONSIDERATION
63. INTUITIVE
64. >>> Person.age > 27 Age is more than 27
65. >>> Person.name %= "Kyle" Name is ? Kyle
66. >>> Person.name ~= "Kyle" Name is LIKE Kyle
67. WHERE TO START?
68. README
70. README
71. PLAYGROUNDS
72. QuerySet().filter(Person.name == "Kyle") .orderBy(Person.name.ascending)
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) }
75. class QuerySet { func orderBy(sortDescriptor:NSSortDescriptor) -> QuerySet { return self } func filter(predicate:NSPredicate) -> QuerySet { return self } subscript(range: Range<Int>) -> QuerySet { return self } }
76. class Person { class var name:Attribute { return Attribute() } } QuerySet().filter(Person.name == "Kyle") .orderBy(Person.name.ascending)
77. !
78. WHAT'S NEXT?
79. WRITING THE REAL IMPLEMENTATION
86. 04:00 AM
91. github.com/kylef/QueryKit
92. twitter.com/kylefuller
94. github.com/kylef/QueryKit twitter.com/kylefuller