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.
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.
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).
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, ...) { ... }
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).
This results in throwing away alias analysis information, because LLVM
does *not* implement reasoning about these conversions yet.
We specialize zero-size types since a `getelementptr` offset will
return us the same pointer, making it broken as a simple counter.
- Made naming schemes consistent between Option, Result and Either
- Changed Options Add implementation to work like the maybe monad (return None if any of the inputs is None)
- Removed duplicate Option::get and renamed all related functions to use the term `unwrap` instead
