Property inheritance
Property inheritance
- Subject: Property inheritance
- From: William Squires <email@hidden>
- Date: Wed, 04 Jul 2012 09:32:58 -0500
Here's my class graph:
Shape (base class - inherits only from NSObject)
LineShape : Shape
RectangleShape : Shape
SquareShape : RectangleShape
In RectangleShape, I define:
@property (nonatomic, assign) CGSize rectSize;
@property (nonatomic, readonly) CGFloat area;
@property (nonatomic, readonly) CGFloat perimeter;
and in RectangleShape.m, I implement these manually, except for rectSize, which I @synthesize:
...
#pragma mark - Non-synthesized accessors
-(CGFloat)area
{
return (self.rectSize.width * self.rectSize.height);
}
-(CGFloat)perimeter
{
return (self.rectSize.width * 2.0 + self.rectSize.height * 2.0);
}
// other stuff...
...
I now want SquareShape to also have the 'area' and 'perimeter' properties, but these should be read/write as there's a direct correlation between the area and the side of the square; ditto for the perimeter. If a subclass (SquareShape) redefines the @property in a superclass as readwrite, are there any 'gotcha's I need to watch out for?
i.e.
SquareShape.h
#import "RectangleShape.h"
@interface SquareShape : RectangleShape
@property (nonatomic, readwrite, assign) CGFloat area;
@property (nonatomic, readwrite, assign) CGFloat perimeter;
@end
SquareShape.m
#import "SquareShape.h"
@implementation SquareShape
#pragma mark - Non-synthesized accessors
-(CGFloat)area
{
return (self.rectSize.width * self.rectSize.height);
}
-(void)setArea:(CGFloat)area
{
CGFloat sideLength = sqrt(area);
CGSize squareSize = CGSizeMake(sideLength, sideLength);
self.rectSize = squareSize;
}
-(CGFloat)perimeter
{
return (self.rectSize.width * 2.0 + self.rectSize.height * 2.0);
}
-(void)setPerimeter:(CGFloat)perimeter
{
CGFloat sideLength = perimeter / 4.0;
CGSize squareSize = CGSizeMake(sideLength, sideLength);
self.rectSize = squareSize;
}
@end
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