Re: Problem with matrices

["Jérôme VUARAND" <jerome.vuarand@...>]

The problem is that your proposition 1 is not following lua table
semantics (that may be considered as a normal semantic since tables
are evrywhere in lua). With the table semantics, matrix.position
returns a reference to the value of the "position" field in the matrix
table, so your proposition 3 would be valid but proposition 1 don't
create a new vector.

To make both work you don't have to return a vector, you can return a
proxy object that acts like a vector but in fact is a reference to the
matrix. It would modify the matrix if you modify it.

2006/5/20, Ivaylo Beltchev <ivo@adelphia.net>:
> Hi
>
> I am trying to create a library for matrix and vector operations. matrix and vector are going to be full userdata.
>
> Vectors are easy. I can define __index to return x, y, or z, and __newindex to set them. Then I can do this:
> 1) a=vector.x -- get the value of x from the vector
> 2) vector.x=0 -- modify the vector
>
> The matrices prove to be trickier. I want to be able to do this, like in C:
> 1) a=matrix.position -- get the value of the position (creates a new vector)
> 2) a=matrix.position.x -- get the value of x from the position
> 3) matrix.position.x=0 -- directly set the value inside the matrix
>
> The problem is that (3) is equivalent to this:
> 3a) a=matrix.position; a.x=0
> It will create a copy of the position, and set its x to 0. The actual matrix will not be modified. It would work in C because in C matrix.position is not the value of the position, but a reference to it.
>
> I can change matrix.position to return a reference vector object, and any changes to it could be forwarded to the matrix. But then (1) will not work as intended. (2) will still work either way.
>
> Any suggestions?
>
> Thanks
> Ivo