Techniques to write DSLs in Swift

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“Clean code reads like well-written prose” – Grady Booch

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@implementation Subscription - (id)init { self = [super init]; if (!self) return nil; self.state = @"pending"; } - (void)activateWithCode:(NSString *)activationCode { if ([self.state isEqualToString:@"pending"] && [self.code isEqualToString:activationCode]) { self.state = @"active"; } } - (void)suspend { if ([self.state isEqualToString:@"active"]) { [self stopBilling]; } } @end IMPLEMENTATION

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LSStateMachine *sm = [[LSStateMachine alloc] init]; LSState *s1 = [[LSState alloc] initWithName:@"pending"]; LSState *s2 = [[LSState alloc] initWithName:@"active"]; [sm addState:s1]; [sm addState:s2]; LSEvent *e1 = [[LSEvent alloc] initWithName:@"activate"]; LSTransition *t1 = [[LSTransition alloc] initWithEvent:e1 from:s1 to:s2]; [sm addTransition:t1]; ABSTRACTION

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TECHNIQUES TO WRITE DSLs IN OBJECTIVE-C

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TECHNIQUES TO WRITE DSLs IN SWIFT

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LUIS SOLANO @luisobo

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DOMAIN-SPECIFIC LANGUAGE

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LANGUAGE PROGRAMMING

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SPECIFIC CONSTRAINT

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TO A CERTAIN DOMAIN CERTAIN TYPE OF PROBLEM

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sm.when("activate", transitionFrom: "pending", to: "active") DSL

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DSL luisobo/StateMachine

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sm.when("activate", transitionFrom: "pending", to: "active") sm.when("suspend", transitionFrom: "active", to: "suspended") sm.when("unsuspend", transitionFrom: "suspended", to: "active") sm.when("terminate", transitionFrom: "active", to: "terminated") sm.when("terminate", transitionFrom: "suspended", to: "terminated") ! sm.before("terminate") { subscription in subscription.terminatedAt = NSDate.date() } ! sm.before("suspend") { subscription in subscription.stopBilling() } DSL

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DECLARATIVE

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imperative

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imperative is ﬁne

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imperative works

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my brain

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my brain cannot handle imperative programming’s scale

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DECLARATIVE

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INTERNAL EXTERNAL INTERNAL

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DSL? WHY TO

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DSL? WHEN TO

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DSL? HOW TO

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SWIFT METHODS luisobo/StateMachine sm.when("activate", transitionFrom: "pending", to: "active")

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SWIFT METHODS luisobo/StateMachine sm.when("activate", transitionFrom: "pending", to: "active")

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METHOD CHAINING stubRequest("GET", "http://hello.com/"). andReturn(200).withBody("hola"); luisobo/Nocilla

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stubRequest("POST", "http://hello.com"). withHeader("Content-Type", "text/plain"). withHeader("X-MY-AWESOME-HEADER", "sisisi"). withBody("Adios!"). andReturn(200). withHeader("Content-Type", "text/plain"). withBody("hola"); METHOD CHAINING luisobo/Nocilla

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EXTENSIONS state.should.eq(“active”)

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EXTENSIONS extension NSObject { var should:Matcher { return Matcher() } }

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[1, 2, 3] [1: “one”, 2: “two”, 3: “three”] ARRAY AND DICTIONARY LITERALS

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stubRequest("GET", “http://hello.com"). withHeaders([“Content-Type": “text/plain", "X-MY-AWESOME-HEADER" : “YEAH!”]). andReturn(200); luisobo/Nocilla ARRAY AND DICTIONARY LITERALS

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.adjustTemperature(24.5).at(“nine"). USING LITERALS WITH YOUR TYPES

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func adjustTemperature(to: Temp) -> Thermostat func at(time: NSDate) -> Thermostat USING LITERALS WITH YOUR TYPES

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protocol FloatLiteralConvertible { ! typealias FloatLiteralType ! class func convertFromFloatLiteral(value: FloatLiteralType) -> Self ! } USING LITERALS WITH YOUR TYPES

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extension Temp: FloatLiteralConvertible { typealias FloatLiteralType = Double class func convertFromFloatLiteral(value: Double) -> Temp { return Temp(degrees: value) } } USING LITERALS WITH YOUR TYPES

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IntegerLiteralConvertible FloatLiteralConvertible StringLiteralConvertible LogicValue StringInterpolationConvertible ArrayLiteralConvertible DictionaryLiteralConvertible USING LITERALS WITH YOUR TYPES 1 3.5 “foo” if myValue “hello \(value)” [1, 2, 3] [“one”: 1, “two”: 2]

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BLOCKS sm.before("terminate") { subscription in subscription.terminatedAt = NSDate.date() } luisobo/StateMachine

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BLOCKS FOR CONTEXT User.defineFactory { f in f["foo"] = "bar" f["password"] = "hunter2" } luisobo/Defactory

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SYNTACTIC SUGAR o.com”).with.body(“Hola”).and.return(200) luisobo/Nocilla

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

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OPERATOR OVERLOAD let s: Speed = 100.meters / 5.seconds

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

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CUSTOM OPERATORS operator infix =>> {}

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=>>

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stubRequest("GET","http://hello.com/") luisobo/Nocilla stubRequest(method:String, url:String)

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stubRequest("GET", "http://hello.com/") stubRequest(“GET", regex(“http://.*\.com”)) luisobo/Nocilla stubRequest(method:String, url:AnyObject)

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stubRequest("POST", NSObject()); stubRequest(“POST”, []); luisobo/Nocilla stubRequest(method:String, url:AnyObject)

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protocol Matchable { func matcher() -> Matcher } ADD PROTOCOL TO EXISTING CLASS luisobo/Nocilla

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extension NSString: Matchable { func matcher() -> Matcher { return StringMatcher(pattern: self) } } ADD PROTOCOL TO EXISTING CLASS

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ADD PROTOCOL TO EXISTING CLASS extension NSRegularExpression: Matchable { func matcher() -> Matcher { return RegexMatcher(pattern: self) } }

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ADD PROTOCOL TO EXISTING CLASS stubRequest("GET", "http://hello.com/") stubRequest(“GET", regex(“http://.*\.com”)) luisobo/Nocilla stubRequest(method:String, url:Matcheable)

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stubRequest("POST", NSObject()]); stubRequest(“POST”,[]]); stubRequest(method:String, url:Matcheable) ADD PROTOCOL TO EXISTING CLASS luisobo/Nocilla

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No content

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Thin layer on top of an abstraction. Limited expressiveness and domain focus. Make your code more maintainable Developer happiness Improved communication Fewer bugs! As seen in TV

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! ! Domain-speciﬁc languages by Martin Fowler brain photo: ﬂickr/_DJ_ redacted font: github/christiannaths Nocilla: github/luisobo StateMachine: github/luisobo Defactory: github/luisobo Kiwi: github/kiwi-bdd metamacros.h github/jspahrsummers THANKS! @luisobo