Add dec!() macro by example

[daniel-pfeiffer]

As discussed, here is a cleaned up, further optimised and integrated new implementation of dec!. It is a completely const and compile-time drop in replacement. This requires Rust 1.79.

Your Result<…String…> is not destructible, i.e. not usable in const. Therefore the new parser has its own Result, that can be transparently converted by ?. This also required splitting try_from_i128_with_scale which thus became simpler.

For now the parser does only exact in i128. Rounding should be addable, if you want to switch parsing completely to this.

Being generic on a smaller type doesn’t currently seem possible in const. Should a benchmark show this to be slower than parsing into u64, the old and new parsers might continue to coexist, till a solution is found.

[paupino]

Sorry for the delay in getting to this - and thank you for putting this together!

Added a couple of comments, however it really boils down to two requested changes I think:

First is to put this behind a feature flag macros. That way, we can remove some unnecessary ambiguity (also, making this an opt in feature). It means prelude will keep working until people have a chance to migrate over.

The other thing we should do is clean up the old macros folder (i.e. remove it completely). Personally, I think having an opinionated way forward is better - also, since it is a separate crate it should be fine to completely remove (i.e. folks can still use the old crate). Of course, this requires some clean up of the documentation to remove the reference to the crate too.

Thanks again!

[paupino]

If we feature flag it, we'd just need to optionally include it here.

[daniel-pfeiffer]

I have added a feature "macro" (singular, as there is only 1, and to differentiate it from your earlier feature) only for the prelude.
I have removed all mentions and uses of rust_decimal_macros.
I have not removed your old sub-crate. I guess you understand better how that is dealt with.

[paupino]

Thank you for your help!