Implementation of std::iter::{Product, Sum}

[dodomorandi]

This PR is relative to the issue 4. This is a
very simple implementation, based on two macros. Maybe a more elegant
solution is possible for these, feel free to suggest.

Two tests for both BigInt and BigUInt have been added, one relative
to the Sum, the other to the Product.

[cuviper]

The CI failure on 1.8 is expected -- we'll have to hold this until I'm ready to bump to num-bigint 0.2.

I wonder, can this be implemented generically? Something like:

impl<T> Sum<T> for BigUint
where BigUint: Add<T, Output=Self> { ... }

Then it should work not just for iterators of BigUint by value and by reference, but also for any of the primitive integers we can add too -- without having to map each to temporary BigUint first!

If this works, I'd just write it directly, without the macro impls.

[cuviper]

I think adding such a generic impl might itself be a breaking change, as someone could have their own impl Sum<Foo> for BigUint already -- but that's ok if we're rolling this into 0.2.

[dodomorandi]

I really liked your suggestion, so I decided to make the two implementations generic. Two additional tests have been added to check against generic Sum and Product (in this case from a vector of i32 or u32, depending from the case).

I want to ask you a thing about conditional compilation: is there a way to check against std features using cfg (iter_arith_traits in this case)? I am quite new with Rust, and I never needed to perform this kind of check... until now. I am not able to find anything useful, but maybe it is just me. Do you have any idea?

[cuviper]

is there a way to check against std features

Sadly, no. So many things would be easier if there were.

[cuviper]

I rebased now that 0.2 has started, and fixed on issue with rust 1.15.

Thanks for implementing this!

bors r+

[bors]

Build succeeded

• continuous-integration/travis-ci/push