num_derive for newtypes

[cuviper]

From @gnzlbg on October 26, 2017 9:18

Say I want to implement some num traits for:

struct R64(f64);

Is there a macro in num_derive to do this? Currently FromPrimitive and ToPrimitive only work on enums.

Copied from original issue: rust-num/num#341

[cuviper]

Those FromPrimitive and ToPrimitive derivations for enums are all we have right now. I would be fine with adding newtype derivations though!

[cuviper]

From @termoshtt on October 27, 2017 6:53

I think proc_macro is better.
I've created a NewType derivation in my crate which derives From, Deref, and DerefMut. IMO, #[derive(Num)] should derive Add, Sub, Mul, Div, and Rem which is required by NumOps (not Num). Remaining traits, i.e. One and Zero should be separated. Hence the interface becomes:

#[derive(One, Zero, Num, PartialEq)]
struct R64(f64);

What do you think?

[cuviper]

From @gnzlbg on October 27, 2017 7:5

I am writing a derive_ops crate where you can do this:

#[derive(stdops)]
#[unary_ops(Not, Neg, Deref, ...)]
#[binary_ops(Add = "Self", Add = "f64", Index = "usize")]
struct R64(f64);

to specify exactly what you want to derive.

It then builds on this to support ops groups:

[derive(stdops)]
[numops]
[binary_ops(DivAssign = "Self")]
struct R64(f64);

If you want I can commit it and maybe we can collaborate. The idea is to derive all ops in stdops for tuple structs with one element easily.

[cuviper]

From @termoshtt on October 27, 2017 7:15

It looks great :)
Does it work on stable rust? I think it will be an independet crate since it will be useful in several cases.

[cuviper]

From @gnzlbg on October 27, 2017 7:19

It works on stable rust (uses only custom derive). Yes I intended it as a separate crate because I think it is generally useful.

[cuviper]

As far as num-derive goes, I was only thinking of derivations for num's own traits. For more general stuff, see also derive_more.

[cuviper]

From @gnzlbg on October 27, 2017 8:7

derive_more doesn't support deriving Mul<R64> for R64 by design. It only supports Mul<f64> for R64.