Empower your Objective-C

Slides for my CMD+R talk http://cmdrconf.com/portfolio/krzysztof-zablocki

Transcript

1. Empower your Objective C
   Krzysztof Zabłocki @merowing_
   

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2. Swift?
   

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3. Objective-C techniques for
   • Less bugs
   • Faster development
   • Higher quality of code
   • More flexibility
   

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4. Technical Bits
   • Key Value Coding
   • Runtime
   • DSL
   • Macros
   • LLVM Attributes
   

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5. Key Value Coding
   • KVC gives us:
   • automatic boxing / unboxing of primitive types
   • collection operators like sum/avg/max, removing need
   to write them
   • more complex operators like unionOfObjects
   • can be applied to sub-objects eg. @sum.price
   • extracting only interesting attributes
   

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6. Key Value Coding
   - (CGFloat)before:(NSArray *)charts
   {
   CGFloat maxValue = CGFLOAT_MIN;
   for(HRBBarGraphChartDescriptor *chart in charts) {
   maxValue = fmaxf(chart.value.floatValue, maxValue);
   }
   return maxValue;
   }
   Turns into:
   - (CGFloat)after:(NSArray *)charts
   {
   return [[charts valueForKeyPath:@"@max.value"] floatValue];
   }
   

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7. Key Value Coding
   - (id )uniqueElementsBefore
   {
   NSMutableArray *allElements = [NSMutableArray new];
   for (ShapeGroup *group in _shapeGroups) {
   for(CCSprite *element in group.elements) {
   if(![allElements containsObject: element]) {
   [allElements addObject:element];
   }
   }
   }
   return [allElements copy];
   }
   Turns into:
   - (id )uniqueElementsAfter
   {
   return [_shapeGroups valueForKeyPath:@"@distinctUnionOfArrays.elements"];
   }
   

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8. Runtime
   • Dynamically create / override functions and classes:
   • Automatically pick up classes implementing specific
   protocol.
   • Intercept methods to log or modify behavior eg. Aspects.
   • Implement similar functions without repetition:
   • eg. findBy{Field}
   • Store context data per instance.
   

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9. Runtime - examples
   • Adding guards around Apple API's misuses:
   • accessing UIKit methods from background threads
   • accessing CoreData context from wrong thread
   • Adding UIGestureRecognizer support to Cocos2D
   • Higher order messaging:
   [[windowsArray do] setHidesOnDeactivate:YES];
   

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10. DSL - Domain Specific Language
    • Simplify code by making it more readable or avoiding
    clutter, eg.
    • KZAsserts automatic NSError generation, assertions and
    graceful error handling with same line of code.
    • KZPropertyMapper implements compile time error
    checking, generates custom bindings, removing need for
    breakable code.
    • Testing/Mocking frameworks
    

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11. DSL - Domain Specific Language
    - (NSError*)method {
    NSParameterAssert([dataFromServer isKindOfClass:[NSDictionary class]]);
    if ([dataFromServer isKindOfClass:[NSDictionary class]]) {
    NSDictionary *userInfo = @{ NSLocalizedDescriptionKey: @"Unable to satisfy condition [dataFromServer isKindOfClass:[NSDictionary class]]"};
    return [NSError errorWithDomain:ErrorDomain code:InternalErrorCode userInfo:userInfo];
    }
    NSParameterAssert([something isKindOfClass:[NSString class]]);
    if ([something isKindOfClass:[NSString class]]) {
    NSDictionary *userInfo = @{ NSLocalizedDescriptionKey: @"Unable to satisfy condition [something isKindOfClass:[NSString class]]"};
    return [NSError errorWithDomain:ErrorDomain code:InternalErrorCode userInfo:userInfo];
    }
    ...
    }
    Into this:
    - (NSError*)method {
    AssertTrueOrReturnError([dataFromServer isKindOfClass:[NSDictionary class]]);
    AssertTrueOrReturnError([something isKindOfClass:[NSString class]]);
    ...
    }
    

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12. DSL - Domain Specific Language
    This is all it takes to map values with type conversion and
    validation:
    [KZPropertyMapper mapValuesFrom:dictionary toInstance:self usingMapping:@{
    @"content_url" : KZBox(URL, contentURL).isRequired(),
    @"full_name" : KZProperty(fullName).lengthRange(5, 12),
    @"videoType" : KZProperty(type),
    @"sub_object" : @{
    @"title" : KZProperty(uniqueID),
    },
    }];
    

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13. DSL - Macros
    #define Macro(param)
    • Generate NSString - @#param turns into @"name"
    • Generate unique symbols by joining:
    NSString *local_##param = #@param; turns into
    NSString *local_name = @"name";
    • Use gcc expression extension to execute few statements:
    ({ result = doSomething(param); result; })
    

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14. DSL - Macros
    #define Macro(param)
    • Generate compilation errors on misspelling of keyPaths/
    properties:
    ({if(NO){ [self param]; }; #@param;})
    np. Macro(name) will return NSString* for a keyPath but only if it
    exists, compile error otherwise.
    

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15. LLVM Attributes - Top 4
    • constructor - similar to +load.
    • NS_REQUIRE_SUPER
    • nonnull - compiler error when trying to explicitly pass null
    • overloadable - multiple functions with same API prototype.
    void __attribute__((overloadable)) KZPShow(CGImageRef image);
    void __attribute__((overloadable)) KZPShow(UIImage *image);
    void __attribute__((overloadable)) KZPShow(NSString *format, ...);
    

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16. Playgrounds?
    

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18. Summary
    • Advanced techniques can save you hours of work
    • Cleaner and more robust code
    • Easier to evolve
    • Fun!
    • With great power comes great responsibility:
    • Design with care
    • Any programming technique can be misused
    

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19. Questions?
    

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20. Thank you!
    Krzysztof Zabłocki
    Follow @merowing_
    

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