Boxing/unboxing problem

Question

The following code snippet crops up quite often in my code where collision rectangles need to be calculated:

bullet.collisionRect.X = (int)bullet.position.X;
bullet.collisionRect.Y = (int)bullet.position.Y;

Is there any way round the unboxing/cast? The collision rects are XNA Rectangles, position X, Y are floats (stored in a Vector2).

Senthilkumar · Answer

Hi Here what is the problem in type casting;? Here you need the conversion. Float and int are the value types but you want to assign the value as expected. But when you do the type conversion there is a chance of data lost. Assume that you are trying to convert 4 byte data into 2 byte definitely there will be some short of data lost.

Vulpes · Answer

In the System.Drawing namespace there are both Rectangle and RectangleF structs which have int and float co-ordinates respectively. I don't know whether XNA is built on similar lines but if it isn't it's no big deal - you're only talking about value type conversions for which performance implications should be minimal.

time and space · Answer

Is there no other way of approaching the problem to achieve the same result? This must be a common situation with C#.

Vulpes · Answer

If you're assigning a float to a property expecting an int then you have no alternative but to convert (or cast) it to an int first. There's no question of boxing here as both int and float are value types. However the former is a 4 byte integer and the latter is a 4 byte floating point value and since assigning the latter to the former may not work at runtime (and will probably lose info) a cast is needed.