Tony Finch – blog

Having tried to make practical use of my multivector multiply, I’m adding a health warning to my notes on vanishing zeroes. (This is my shamefaced grin.)

There’s a general rule with Rust that if the compiler is making things hard for you, it’s usually right, and you should pay attention.

The problem with my type system hackery is kind of right there in my description of what was difficult about making it work: the requirements in the trait bounds have to be spelled out in full.

I had trouble with the enormous trait bounds that I needed in order to use the small Zero and Num overloads; the same trouble will occur, but bigger, for anyone who tries to use the overloaded multivector multiply in a generic way.

This means that application code will only be tolerable if it uses concrete types at function boundaries, and avoids generic overloading except to support type inference within functions. This is not very far from what I had in mind, but less flexible.

It’s worse for mid-level code which provides higher-level multivecor operations. I wanted to combine generic multivector primitives into generic higher-level operations, but the types make this too awful to contemplate. It might be possible to rescue it by extending the wide-and-shallow approach to these operations, i.e. define them all in the same style as multiplication.

So it’s sad and somewhat embarrassing that it didn’t work out, but I did learn quite a lot about Rust in the process :-)

Anyway, after reflecting on my mistakes, I’m putting this aside for now, and I’m circling around to vector in on my 3D graphics project from another angle.