The trait will keep the `Iterator` naming, but a more concise module
name makes using the free functions less verbose. The module will define
iterables in addition to iterators, as it deals with iteration in
general.
The message of the first commit explains (edited for changed trait name):
The trait `ExactSize` is introduced to solve a few small niggles:
* We can't reverse (`.invert()`) an enumeration iterator
* for a vector, we have `v.iter().position(f)` but `v.rposition(f)`.
* We can't reverse `Zip` even if both iterators are from vectors
`ExactSize` is an empty trait that is intended to indicate that an
iterator, for example `VecIterator`, knows its exact finite size and
reports it correctly using `.size_hint()`. Only adaptors that preserve
this at all times, can expose this trait further. (Where here we say
finite for fitting in uint).
---
It may seem complicated just to solve these small "niggles",
(It's really the reversible enumerate case that's the most interesting)
but only a few core iterators need to implement this trait.
While we gain more capabilities generically for some iterators,
it becomes a tad more complicated to figure out if a type has
the right trait impls for it.
This removes the stacking of type parameters that occurs when invoking
trait methods, and fixes all places in the standard library that were
relying on it. It is somewhat awkward in places; I think we'll probably
want something like the `Foo::<for T>::new()` syntax.
If they are on the trait then it is extremely annoying to use them as
generic parameters to a function, e.g. with the iterator param on the trait
itself, if one was to pass an Extendable<int> to a function that filled it
either from a Range or a Map<VecIterator>, one needs to write something
like:
fn foo<E: Extendable<int, Range<int>> +
Extendable<int, Map<&'self int, int, VecIterator<int>>>
(e: &mut E, ...) { ... }
since using a generic, i.e. `foo<E: Extendable<int, I>, I: Iterator<int>>`
means that `foo` takes 2 type parameters, and the caller has to specify them
(which doesn't work anyway, as they'll mismatch with the iterators used in
`foo` itself).
This patch changes it to:
fn foo<E: Extendable<int>>(e: &mut E, ...) { ... }
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).
Change the former repetition::
for 5.times { }
to::
do 5.times { }
.times() cannot be broken with `break` or `return` anymore; for those
cases, use a numerical range loop instead.
Drop the "Iterator" suffix for the the structs in std::iterator.
Filter, Zip, Chain etc. are shorter type names for when iterator
pipelines need their types written out in full in return value types, so
it's easier to read and write. the iterator module already forms enough
namespace.
With the recent fixes to method resolution, we can now remove the
dummy type parameters used as crutches in the iterator module.
For example, the zip adaptor type is just ZipIterator<T, U> now.
.peek_next() needs to check the element counter just like the .next()
and .next_back() iterators do.
Also clarify .insert_next() doc w.r.t double ended iteration.
Factor out internal methods for pop/push ~Node<T>, This allows moving
nodes instead of destructuring and allocating new.
Make use of this in .merge() so that it requires no allocations when
merging two DList.
Unify the mutable iterators too. Switch the ListInsertion trait to use
method .insert_next() and .peek_next() for list mutation. .insert_next()
inserts an element into the list that will not appear in iteration, of
course; so the length of the iteration can not change during iteration.
Did not properly allow runs from the `other` list to be merged in. The
test case was using a wrong expected value.
Edited docs for merge so they explain more clearly what it does.
Also make sure insert_ordered is marked pub.
An iterator that allows mutating the list is very useful but needs care
to not be unsound. ListIteration exposes only insert_before (used for
insert_ordered) and peek_next so far.
