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.
The trait `ExactSizeHint` 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
`ExactSizeHint` 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).
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.
Add size_hint() to a few Iterators that were missing it.
Update a couple of existing size_hint()s to use checked_add() instead of
saturating_add() for the upper bound.
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).
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.
According to #7887, we've decided to use the syntax of `fn map<U>(f: &fn(&T) -> U) -> U`, which passes a reference to the closure, and to `fn map_move<U>(f: &fn(T) -> U) -> U` which moves the value into the closure. This PR adds these `.map_move()` functions to `Option` and `Result`.
In addition, it has these other minor features:
* Replaces a couple uses of `option.get()`, `result.get()`, and `result.get_err()` with `option.unwrap()`, `result.unwrap()`, and `result.unwrap_err()`. (See #8268 and #8288 for a more thorough adaptation of this functionality.
* Removes `option.take_map()` and `option.take_map_default()`. These two functions can be easily written as `.take().map_move(...)`.
* Adds a better error message to `result.unwrap()` and `result.unwrap_err()`.
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.
Implement RAI where possible for iterator adaptors such as Map,
Enumerate, Skip, Take, Zip, Cycle (all of the requiring that the adapted
iterator also implements RAI).
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.
