Techniques to write DSLs in Objective-C

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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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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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STATE_MACHINE(^(LSStateMachine *sm) { sm.initialState = @"pending"; ! [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" do:^(Subscription *subscription){ subscription.terminatedAt = [NSDate date]; }]; [sm after:@"suspend" do:^(Subscription *subscription) { [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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[sm when:@“activate" transitionFrom:@"pending" to:@"active"]; OBJECTIVE-C METHODS luisobo/StateMachine

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[sm when:@“activate" transitionFrom:@"pending" to:@"active"]; OBJECTIVE-C METHODS luisobo/StateMachine

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[[sut.state should] equal:@"active"]; METHOD CHAINING kiwi-bdd/Kiwi

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METHOD CHAINING (dot notation) 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 (dot notation) luisobo/Nocilla

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@[] @{} 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); METHOD CHAINING (dot notation) luisobo/Nocilla

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#define MACROS

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metamacros.h jspahrsummers/libextobjc #define metamacro_concat #define metamacro_if_eq #define metamacro_foreach #define metamacro_head

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WHERE DO I PUT MY DSL?

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DSL ENTRY POINT FACTORIES { ! // Your DSL goes here. ! } luisobo/Defactory

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DSL ENTRY POINT __attribute__((constructor)) void MyAwesomeEntryPoint(void) { // Your DSL goes here. ! } luisobo/Defactory

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__COUNTER__ DSL ENTRY POINT

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DSL ENTRY POINT #define _CONCAT(a,b) a##b #define _LABEL(a) _CONCAT(MyFunction, a) #define _UNIQUE_NAME _LABEL(__COUNTER__) luisobo/Defactory

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DSL ENTRY POINT #define FACTORIES\ __attribute__((constructor))\ void _UNIQUE_NAME(void) luisobo/Defactory

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DSL ENTRY POINTS FACTORIES { ! } ! FACTORIES { ! } luisobo/Defactory

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BLOCKS [sm before:@"terminate" do:^(Subscription *subscription){ subscription.terminatedAt = [NSDate date]; }]; luisobo/StateMachine

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BLOCKS FOR CONTEXT [LSUser defineFactory:^(LSFactory *f) { f[@"username"] = @"foo"; f[@"password"] = @"hunter2"; }]; luisobo/Defactory

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BLOCKS FOR CONTEXT STATE_MACHINE(^(LSStateMachine *sm) { sm.initialState = @"pending"; ! [sm when:@"activate" transitionFrom:@"pending" to:@"active"]; ! // ... }); luisobo/StateMachine

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CATEGORIES [[sut.state should] equal:@"active"]; kiwi-bdd/Kiwi

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SCOPES @interface SomeClass () ! @property NSDateFormatter *formatter; ! @end

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SCOPES LAZY(formatter, [[NSDateFormatter alloc] init]); @implementation SomeClass ! ! ! @end

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SCOPES { ! // Hey, this is an inner scope ! }

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SCOPES @implementation SomeClass ! ! ! ! ! ! @end LAZY(formatter, { NSDateFormatter *f = [NSDateFormatter new]; [f setDateFormat:@"%Y-%m-%d %H:%M:%S"]; f; });

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

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stubRequest(@“POST”, nil); stubRequest(NSString *method, NSString *url); luisobo/Nocilla

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__attribute__((nonnull (1, 2)); eable> url) COMPILE-TIME NULL CHECK luisobo/Nocilla

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stubRequest(@“POST”, nil); stubRequest(NSString *method, id url) __attribute__((nonnull (1, 2)); luisobo/Nocilla COMPILE-TIME NULL CHECK

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stubRequest(NSString *method, NSString *url); stubRequest(@"GET", @"http://hello.com/") luisobo/Nocilla

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

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stubRequest(@"POST", [NSObject new]); stubRequest(@“POST”, @[]); stubRequest(NSString *method, id url) luisobo/Nocilla

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@protocol LSMatcheable ! - (LSMatcher *)matcher; ! @end ADD PROTOCOL TO EXISTING CLASS luisobo/Nocilla

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@interface NSString (Matcheable) ! @end ! @implementation NSString (Matcheable) ! - (LSMatcher *)matcher { return [[LSStringMatcher alloc] initWithString:self]; } ! @end ! ADD PROTOCOL TO EXISTING CLASS

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@interface NSRegularExpression (Matcheable) ! @end ! @implementation NSRegularExpression (Matcheable) ! - (LSMatcher *)matcher { return [[LSRegexMatcher alloc] initWithRegex:self]; } ! @end ! ADD PROTOCOL TO EXISTING CLASS

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

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stubRequest(@"POST", [NSObject new]); stubRequest(@“POST”,@[]]); stubRequest(NSString *method, id url) 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