ShapeArea

AreaCalculator.h

#import <Foundation/Foundation.h>

@interface AreaCalculator : NSObject

+(float) calculateArea:(NSArray*)shapes;

@end

AreaCalculator.m

@implementation AreaCalculator

+(float) calculateArea:(NSMutableArray*)shapes{
    
    float totalArea = 0.0;
    
    for (Shape *shape in shapes){
        totalArea += [shape getArea];
    }
    
    return totalArea;
}

@end


/* This is the way that breaks open/closed
 
+(float) calculateArea:(NSMutableArray*)shapes{
    
    float totalArea = 0.0;
    
    for (Shape *shape in shapes){
        if ([shape isKindOfClass:[Rectangle class]]){
            Rectangle *rect = (Rectangle*)shape;
            totalArea += rect.width * rect.height;
        } else {
            Circle *circle = (Circle*)shape;
            totalArea += circle.radius * 2 * 3.1415926;
        }
        
    }
    
    return totalArea;
}
 */

Circle.h

@interface Circle : Shape

@property(nonatomic, assign) int radius;

@end

Circle.m

@implementation Circle

-(float) getArea{
    return self.radius * 2 * 3.1415926;
}

@end

main.m

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        
        Rectangle *rectangle1 = [[Rectangle alloc] init];
        rectangle1.width = 2;
        rectangle1.height = 3;
        
        Rectangle *rectangle2 = [[Rectangle alloc] init];
        rectangle2.width = 4;
        rectangle2.height = 6;
        
        Circle *circle = [[Circle alloc] init];
        circle.radius = 7;
        
        Square *square = [[Square alloc] init];
        square.width = 4;
        square.height = 3; //This is what breaks Liskov's
        
        NSArray *rectArray = @[rectangle1, rectangle2, circle, square];
        
        NSLog(@"total area: %.2f", [AreaCalculator calculateArea:rectArray] );
        
        
    }
    return 0;
}

Rectangle.h

@interface Rectangle : Shape

@property(nonatomic,assign) int width;
@property(nonatomic,assign) int height;

@end

Shape.h

@interface Shape : NSObject

-(float) getArea;

@end

Shape.m

@implementation Shape

-(float) getArea{
    [NSException raise:@"getArea called on Shape, asshole" format:@"invliad", nil];
    return 0.0;
}

@end

Square.h

@interface Square : Rectangle

@end

Square.m

@implementation Square

-(float)getArea{
    return pow(self.width, 2);
}

@end