How did you solve the problem in your matrix libraries of overloading a single o...

pcwalton · on July 25, 2012

I was about to say "you can't do it", but I think you can -- the trick is to use a bounded generic implementation. Once "Mul" becomes a trait, you'll be able to say this:

    trait MatrixMultiplyRHS<Result> {
        fn mul(matrix: Matrix) -> Result;
    }

    impl<RHS:MatrixMultiplyRHS<Result>,Result> Matrix : Mul<RHS, Result> {
        fn mul(rhs: RHS) -> Result {
            rhs.mul(self)
        }
    }

    impl float : MatrixMultiplyRHS<Matrix> {
        fn mul(matrix: Matrix) -> Matrix {
            // ...implementation of matrix scalar multiply...
        }
    }

    impl Vector : MatrixMultiplyRHS<Vector> {
        fn mul(matrix: Matrix) -> Vector {
            // ... implementation of matrix multiply for vectors ...
        }
    }

    impl Matrix : MatrixMultiplyRHS<Matrix> {
        fn mul(matrix: Matrix) -> Matrix {
            // ... implementation of matrix multiply for matrices ...
        }
    }

It's admittedly a bit awkward, but maybe that's OK to discourage overloading unless you actually need it. Still, your point was very interesting -- I didn't realize this was possible! -- and I'll spread it around the team.

bjz · on July 25, 2012

Ahh neat.

Just as a warning, I've already aired this topic on github, so maybe that might be a good place to discuss it: https://github.com/mozilla/rust/issues/2961

I don't want to cause a fuss. While Rust might not work for my needs/wants/desires, that's ok. I highly respect those who don't attempt to please everyone. :)

LinaLauneBaer · on July 25, 2012

I don't know rust but rust seems very much like C++.

Did you have a look at the Eigen library (C++)?

http://eigen.tuxfamily.org/dox/TutorialMatrixClass.html

I have never worked with this library but it seems to me that they have not the problems you described. Maybe having a look at it brings up some new ideas...

bjz · on July 25, 2012

Although on superficial level it shares the AGOL/C-style syntax, Rust is a very different language from C++. Some things are possible or easier in Rust as opposed to C++ and vice-versa. Copying directly from a C++ library would be difficult, and wouldn't take advantage of Rust's unique strengths.

LinaLauneBaer · on July 25, 2012

Okay. Thanks for the info. I just had a quick look at Rusts wikipedia entry and saw that it has been influenced by C++. But as you pointed out, this might not mean much...