Arithmetic operations with reference semantics

[cohomology]

In the implementation of complex, the Add, Sub, etc. for references are forwarded via clone() for values. This is very bad for types which are expensive to copy. In my example, I use Complex<Ratio<BigInt>>.

Can the code be refactored in such a way, that no clone() is necessary? I guess the different arithmetic operations have to be coded out and not forwarded.

I could try that, if there is no objection against that ...

[cuviper]

The main problem is that we added all of those implementations with just T: Clone + Num, and it's a breaking change to add additional constraints. To implement ops directly on references, we would probably want to use NumRef, NumAssignRef, and RefNum.

[cuviper]

In my example, I use Complex<Ratio<BigInt>>.

Note, Ratio also implements reference ops by cloning, which means that changing Complex alone wouldn't really help you.

I started looking at this for 0.3 (#70), but I'm skeptical. It requires a lot of code duplication on our part to directly implement each op with/without clones, and the additional T: NumRef + ... requirements end up propagating widely. The latter will affect all generic users too, sadly.