Address discussion with acrichto; inherit DoubleEndedIterator so that
`.rposition()` can be a default method, and that the nische of the trait
is clear. Use assertions when using `.size_hint()` in reverse enumerate
and `.rposition()`
This is a generalization of the vector .rposition() method, to all
double-ended iterators that have the ExactSizeHint trait.
This resolves the slight asymmetry around `position` and `rposition`
* position from front is `vec.iter().position()`
* position from the back was, `vec.rposition()` is now `vec.iter().rposition()`
Additionally, other indexed sequences (only `extra::ringbuf` I think),
will have the same method available once it implements ExactSizeHint.
Use Eq + Ord for lexicographical ordering of sequences.
For each of <, <=, >= or > as R, use::
[x, ..xs] R [y, ..ys] = if x != y { x R y } else { xs R ys }
Previous code using `a < b` and then `!(b < a)` for short-circuiting
fails on cases such as [1.0, 2.0] < [0.0/0.0, 3.0], where the first
element was effectively considered equal.
Containers like &[T] did also implement only one comparison operator `<`,
and derived the comparison results from this. This isn't correct either for
Ord.
Implement functions in `std::iterator::order::{lt,le,gt,ge,equal,cmp}` that all
iterable containers can use for lexical order.
We also visit tuple ordering, having the same problem and same solution
(but differing implementation).
Fixes most of #4989. I didn't add Persistent{Set,Map} since the only
persistent data structure is fun_treemap and its functionality is
currently too limited to build a trait out of.
I think it's WIP - but I wanted to ask for feedback (/cc @thestinger)
I had to move the impl of FromIter for vec into extra::iter because I don't think std can depend on extra, but that's a bit messed up. Similarly some FromIter uses are gone now, not sure if this is fixable or if I made a complete mess here..
the `test/run-pass/class-trait-bounded-param.rs` test was xfailed and
written in an ancient dialect of Rust so I've just removed it
this also removes `to_vec` from DList because it's provided by
`std::iter::to_vec`
an Iterator implementation is added for OptVec but some transitional
internal iterator methods are still left
