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DESIGNING | BUILDING DSLS IN SWIFT @KYLEFULLER

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BASE

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SHAPE

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WHAT IS A DSL?

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DOMAIN SPECIFIC LANGUAGE

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PROGRAMMING LANGUAGE

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DECLARATIVE

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SPECIFIC

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NOT GENERIC

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FREEDOM

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BUGS

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NSPredicate

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NAME EQUALS Kyle

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USING NSPredicate

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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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IMPERATIVE

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FRUSTRATING

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

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EASY TO WRITE BUGS

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

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

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INELEGANT

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DSLS

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

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SWIFT

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CUSTOM OPERATORS

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(Something) == (Something else)

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

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Person.name == "Kyle"

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IDEA

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CORE DATA DSL

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MAKING A QUERY IN CORE DATA

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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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6 LINES

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

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1 LINE

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REFACTORING

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

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

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BUILD SUCCESSFUL

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*** 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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Keypath age not found in entity

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

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

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COULD WE DO THIS BETTER WITH A DSL?

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SAY NO TO HARD CODED STRINGS

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Person.age.ascending

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READABILITY

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SAFE

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DSLS ARE !

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!

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DON'T ABUSE THE POWER Swift HAS GIVEN US.

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GOING TOO FAR

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BAD

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Person.name %= "Kyle"

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CONSIDERATION

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INTUITIVE

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

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

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

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WHERE TO START?

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README

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README

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PLAYGROUNDS

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

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

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!

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WHAT'S NEXT?

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WRITING THE REAL IMPLEMENTATION

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04:00 AM

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github.com/kylef/QueryKit

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twitter.com/kylefuller

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