iOS Objective-C: NSMutable Array returns garbage - objective-c

Question

I'm trying to take a C-style vector and convert it into an NSMutable array object.
Here's the function:
+(NSMutableArray*)arrayFromPoints:(vector<Point2f>&)points
{
NSMutableArray* pointArray = [[NSMutableArray alloc] init];
for (int i=0;i<points.size();i++)
{
Point2f point = points[i];
JBPoint* point2 = [[JBPoint alloc]initWithX:point.x andY:point.y];
[pointArray addObject:point2];
}
return pointArray;
}
Custom point class:
#implementation JBPoint
float _x;
float _y;
-(id) initWithX:(float)x andY:(float)y
{
if (self=[super init])
{
_x = x;
_y=y;
}
return self;
}
-(float)x{ return _x;}
-(float)y {return _y;}
#end
Test output:
for (JBPoint* pnt in array)
{
NSLog(#"%f, %f", pnt.x, pnt.y);
}
I except it to output the array, but every time it just gives me the last value! does anyone know why?
I thought that they were maybe pointing to the same object, but they have different memory addresses.

Answer 1

So I figured out the problem. float _x;
float _y; where being treated like class variables instead of instance variables. Changed the class to:
#interface JBPoint()
{
float _x;
float _y;
}
#end
#implementation JBPoint
-(id) initWithX:(float)x andY:(float)y
{
if (self=[super init])
{
_x = x;
_y=y;
}
return self;
}
-(float)x{ return _x;}
-(float)y {return _y;}
#end

Answer 2

if you wrote
#property (nonatomic, readonly) float x;
#property (nonatomic, readonly) float y;
in your header file you wouldn't need to declare the instance variables (and would have avoided the issue here) and you could delete the getter methods your wrote as that would all be generated by the compiler for you and your custom init method would continue to work (with the most recent compiler).
Its a good idea to do this because:
less code
your intent is clear - 2 variables that are readonly for clients
follows language conventions
If you are using an older compiler (an older version of Xcode) then you would also have to #synthesize the accessors like this:
#synthesize x = _x;
Some interesting asides:
With the most recent complier you didn't need the class extension.
#implementation{
float _x;
float _y;
}
would also have worked.
As referenced in WWDC 2012 session video 413, the current recommended pattern to write an init method is:
...
self = [super init];
if (self) {
...
}
return self;