error: invalid lvalue in assignment

Subject: error: invalid lvalue in assignment
From: Don Arnel <email@hidden>
Date: Mon, 25 Aug 2008 19:25:14 -0400
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Hello everyone!

I'm having a problem using a property for one of my custom class objects.

I have a class like this:


INTERFACE (MyObject.h):
-----------------------------------

typedef struct {
	float x;
	float y;
} Vector2D;

@interface myObject : NSObject {
	Vector2D _position;
}

@property Vector2D position;

@end


IMPLEMENTATION (MyObject.m):
---------------------------------------------

@implementation myObject

@synthesize position=_position;

- (id)init
{
	if ((self=[super init]) != nil) {
		_position.x = 0.0;
		_position.y = 0.0;
	}
	return self;
}

@end

I tried to modify the "position" property in another file after creating an object but I get this error:

	obj.position.x += 1.0;
	(x error: invalid lvalue in assignment)

I can assign the value without a problem:

		float x = obj.position.x;
		x += 1.0;

But then this is also a no-no:

		obj.position.x = x;

Anyone have any ideas as to why the first assignment gives an error?

Thanks for any and all help.
- Don


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