Iterator Trait Parity

Here is a copy of the current Iterator trait along with some annotations on each of its methods:

pub trait Iterator {
    type Item;
    fn next(&mut self) -> Option<Self::Item>;

N/A    fn size_hint(&self) -> (usize, Option<usize>) { ... }
DONE    fn count(self) -> usize { ... }
N/A     fn last(self) -> Option<Self::Item> { ... }
N/A     fn nth(&mut self, n: usize) -> Option<Self::Item> { ... }
DONE    fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where U: IntoIterator<Item=Self::Item> { ... }
DONE    fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where U: IntoIterator { ... }
DONE    fn map<B, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> B { ... }
DONE    fn filter<P>(self, predicate: P) -> Filter<Self, P> where P: FnMut(&Self::Item) -> bool { ... }
DONE    fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where F: FnMut(Self::Item) -> Option<B> { ... }
DONE    fn enumerate(self) -> Enumerate<Self> { ... }
N/A     fn peekable(self) -> Peekable<Self> { ... }
    fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where P: FnMut(&Self::Item) -> bool { ... }
    fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where P: FnMut(&Self::Item) -> bool { ... }
EASY    fn skip(self, n: usize) -> Skip<Self> { ... }
        - seems easy on a ExactLengthIterator; just split_at(n) and discard one side, right?
        - otherwise, seems very hard
EASY    fn take(self, n: usize) -> Take<Self> { ... }
        - seems easy on a ExactLengthIterator; just split_at(len - n) and discard one side, right?
        - otherwise...seems hard.
HARD    fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where F: FnMut(&mut St, Self::Item) -> Option<B> { ... }
DONE    fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where F: FnMut(Self::Item) -> U, U: IntoIterator { ... }
MEH     fn fuse(self) -> Fuse<Self> { ... }
DONE    fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item) -> () { ... }
MEH     fn by_ref(&mut self) -> &mut Self { ... }
#124    fn collect<B>(self) -> B where B: FromIterator<Self::Item> { ... }
HMM     fn partition<B, F>(self, f: F) -> (B, B) where B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool { ... }
        - I've always thought this signature was wrong. Trying to remember why. =)
        - At minimum, it should permit two distinct kinds of collections.
        - Still, it's interesting that the current FromParallelIterator can't support this.
DONE    fn fold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B { ... }
DONE    fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool { ... }
DONE    fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool { ... }
PARTIAL    fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool { ... }
PARTIAL    fn position<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool { ... }
PARTIAL    fn rposition<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool, Self: ExactSizeIterator + DoubleEndedIterator { ... }
DONE    fn max(self) -> Option<Self::Item> where Self::Item: Ord { ... }
DONE    fn min(self) -> Option<Self::Item> where Self::Item: Ord { ... }
EASY    fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B { ... }
EASY    fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B { ... }
EASY?   fn rev(self) -> Rev<Self> where Self: DoubleEndedIterator { ... }
        - would require Exact iterator
        - maybe easy? maybe requires tweaks to producer...
HMM     fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Iterator<Item=(A, B)> { ... }
        - like partition, a bit tricky
DONE    fn cloned<'a, T>(self) -> Cloned<Self> where Self: Iterator<Item=&'a T>, T: 'a + Clone { ... }
    fn cycle(self) -> Cycle<Self> where Self: Clone { ... }
DONE    fn sum<S>(self) -> S where S: Sum<Self::Item> { ... }
DONE    fn product<P>(self) -> P where P: Product<Self::Item> { ... }
EASY    fn cmp<I>(self, other: I) -> Ordering where I: IntoIterator<Item=Self::Item>, Self::Item: Ord { ... }
EASY    fn partial_cmp<I>(self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
EASY    fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item> { ... }
EASY    fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item> { ... }
EASY    fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
EASY    fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
EASY    fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
EASY    fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item> { ... }
}