Techniques to write DSLs in Objective-C

"Clean code reads like well-written prose" - Grady Booch

Programming languages can be a really powerful tool, so powerful they allow
us to make mistakes and introduce bugs in our programs. So powerful they
allow us to poorly design or programs, making them hard to modify or extend.

A domain-specific language is a small language that allows us to solve
problems in a particular domain and because they are both constrained and
declarative there is almost no room for mistakes. DSLs make our code much
easier to read, maintain and modify.

This talk will cover:
* The main advantages and disadvantages of using DSLs
* When to use them
* How to raise the level of abstraction and separate implementation details
from expected behavior
* What are the main techniques to write DSLs in Objective-C.

Transcript

1. “Clean code reads like well-written prose” – Grady Booch
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4. @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
5. 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
6. TECHNIQUES TO WRITE DSLs IN OBJECTIVE-C
7. LUIS SOLANO @luisobo
8. DOMAIN-SPECIFIC LANGUAGE
9. LANGUAGE PROGRAMMING
10. SPECIFIC CONSTRAINT
11. TO A CERTAIN DOMAIN CERTAIN TYPE OF PROBLEM
12. 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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14. 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
15. [sm when:@“activate" transitionFrom:@"pending" to:@"active"]; DSL
16. DSL luisobo/StateMachine
17. 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
18. asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla
19. asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla asjdañlksjdlaksjdñlak asjdañlksjdla Semantic model Domain-specfic language
20. DECLARATIVE
21. imperative
22. imperative is fine
23. imperative works
24. my brain
25. my brain cannot handle imperative programming’s scale
26. DECLARATIVE
27. INTERNAL EXTERNAL INTERNAL
28. DSL? WHY TO
29. DSL? WHEN TO
30. DSL? HOW TO
31. [sm when:@“activate" transitionFrom:@"pending" to:@"active"]; OBJECTIVE-C METHODS luisobo/StateMachine
32. 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]; OBJECTIVE-C METHODS luisobo/StateMachine
33. [sm when:@“activate" transitionFrom:@"pending" to:@"active"]; OBJECTIVE-C METHODS luisobo/StateMachine
34. [[sut.state should] equal:@"active"]; METHOD CHAINING kiwi-bdd/Kiwi
35. METHOD CHAINING (dot notation) stubRequest(@"GET", @"http://hello.com/"). andReturn(200).withBody(@"hola"); luisobo/Nocilla
36. 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
37. @[] @{} ARRAY AND DICTIONARY LITERALS
38. stubRequest(@"GET", @“http://hello.com"). withHeaders(@{@"Content-Type" : @“text/plain", @"X-MY-AWESOME-HEADER" : @“YEAH!”}). andReturn(200); METHOD CHAINING (dot notation) luisobo/Nocilla
39. #define MACROS
40. metamacros.h jspahrsummers/libextobjc #define metamacro_concat #define metamacro_if_eq #define metamacro_foreach #define metamacro_head
41. WHERE DO I PUT MY DSL?
42. DSL ENTRY POINT FACTORIES { ! // Your DSL goes here. ! } luisobo/Defactory
43. DSL ENTRY POINT __attribute__((constructor)) void MyAwesomeEntryPoint(void) { // Your DSL goes here. ! } luisobo/Defactory
44. __COUNTER__ DSL ENTRY POINT
45. DSL ENTRY POINT #define _CONCAT(a,b) a##b #define _LABEL(a) _CONCAT(MyFunction, a) #define _UNIQUE_NAME _LABEL(__COUNTER__) luisobo/Defactory
46. DSL ENTRY POINT #define FACTORIES\ __attribute__((constructor))\ void _UNIQUE_NAME(void) luisobo/Defactory
47. DSL ENTRY POINTS FACTORIES { ! } ! FACTORIES { ! } luisobo/Defactory
48. BLOCKS [sm before:@"terminate" do:^(Subscription *subscription){ subscription.terminatedAt = [NSDate date]; }]; luisobo/StateMachine
49. BLOCKS FOR CONTEXT [LSUser defineFactory:^(LSFactory *f) { f[@"username"] = @"foo"; f[@"password"] = @"hunter2"; }]; luisobo/Defactory
50. BLOCKS FOR CONTEXT STATE_MACHINE(^(LSStateMachine *sm) { sm.initialState = @"pending"; ! [sm when:@"activate" transitionFrom:@"pending" to:@"active"]; ! // ... }); luisobo/StateMachine
51. CATEGORIES [[sut.state should] equal:@"active"]; kiwi-bdd/Kiwi
52. SCOPES @interface SomeClass () ! @property NSDateFormatter *formatter; ! @end
53. SCOPES LAZY(formatter, [[NSDateFormatter alloc] init]); @implementation SomeClass ! ! ! @end
54. SCOPES { ! // Hey, this is an inner scope ! }
55. SCOPES @implementation SomeClass ! ! ! ! ! ! @end LAZY(formatter, { NSDateFormatter *f = [NSDateFormatter new]; [f setDateFormat:@"%Y-%m-%d %H:%M:%S"]; f; });
56. SYNTACTIC SUGAR o.com”).with.body(@“Hola”).and.return(200 luisobo/Nocilla
57. stubRequest(@“POST”, nil); stubRequest(NSString *method, NSString *url); luisobo/Nocilla
58. __attribute__((nonnull (1, 2)); eable> url) COMPILE-TIME NULL CHECK luisobo/Nocilla
59. stubRequest(@“POST”, nil); stubRequest(NSString *method, id<LSMatcheable> url) __attribute__((nonnull (1, 2)); luisobo/Nocilla COMPILE-TIME NULL CHECK
60. stubRequest(NSString *method, NSString *url); stubRequest(@"GET", @"http://hello.com/") luisobo/Nocilla
61. stubRequest(NSString *method, id url) stubRequest(@"GET", @"http://hello.com/") stubRequest(@“GET", regex(@“http://.*\.com”)) luisobo/Nocilla
62. stubRequest(@"POST", [NSObject new]); stubRequest(@“POST”, @[]); stubRequest(NSString *method, id url) luisobo/Nocilla
63. @protocol LSMatcheable <NSObject> ! - (LSMatcher *)matcher; ! @end ADD PROTOCOL TO EXISTING CLASS luisobo/Nocilla
64. @interface NSString (Matcheable) <LSMatcheable> ! @end ! @implementation NSString (Matcheable) ! - (LSMatcher *)matcher { return [[LSStringMatcher alloc] initWithString:self]; } ! @end ! ADD PROTOCOL TO EXISTING CLASS
65. @interface NSRegularExpression (Matcheable) <LSMatcheable> ! @end ! @implementation NSRegularExpression (Matcheable) ! - (LSMatcher *)matcher { return [[LSRegexMatcher alloc] initWithRegex:self]; } ! @end ! ADD PROTOCOL TO EXISTING CLASS
66. stubRequest(NSString *method, id<LSMatcheable> url) ADD PROTOCOL TO EXISTING CLASS stubRequest(@"GET", @"http://hello.com/") stubRequest(@“GET", regex(@“http://.*\.com”)) luisobo/Nocilla
67. stubRequest(@"POST", [NSObject new]); stubRequest(@“POST”,@[]]); stubRequest(NSString *method, id<LSMatcheable> url) ADD PROTOCOL TO EXISTING CLASS luisobo/Nocilla
69. 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
70. ! ! 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