* Remove type parameters from `IteratorExt::cloned`
* Rename `IntoIterator::Iter` to `IntoIterator::IntoIter`
* Mark `IntoIterator::into_iter` as stable (but not the trait, only the method).
When self.start > self.end, these iterators simply return None,
so we adjust the size_hint to just return zero in this case.
Certain optimizations can be implemented in and outside libstd if we
know we can trust the size_hint for all inputs to for example
Range<usize>.
This corrects the ExactSizeIterator implementations, which IMO were
unsound and incorrect previously, since they allowed a range like (2..1)
to return a size_hint of -1us in when debug assertions are turned off.
Right now it is not possible to write a `for` loop without opting-in to the
`core` feature due to the way they're expanding (calling
`::std::iter::IntoIterator::into_iter`). There are some planned tweaks to the
`IntoIterator` trait (adding an `Item` associated type) which will cause
implementations of `IntoIterator` to break, but the *usage* of the trait is
currently stable.
This commit marks the method `into_iter` as stable as the name will not be
changing, nor the fact that it takes no arguments and returns one type (which is
determiend by the `Self` type). This means that usage of `for` loops is now
stable but manual implementations of the `IntoIterator` trait will continue to
be unstable.
This is in preparation for stabilization of the `IntoIterator` trait. All
implementations and references to `Iter` need to be renamed to `IntoIter`.
[breaking-change]
When self.start > self.end, these iterators simply return None,
so we adjust the size_hint to just return zero in this case.
Certain optimizations can be implemented in and outside libstd if we
know we can trust the size_hint for all inputs to for example
Range<usize>.
This corrects the ExactSizeIterator implementations, which IMO were
unsound and incorrect previously, since they allowed a range like (2..1)
to return a size_hint of -1us in when debug assertions are turned off.
This removes the `ByRef` iterator adaptor to stay in line with the changes to
`std::io`. The `by_ref` method instead just returns `&mut Self`.
This also removes the implementation of `Iterator for &mut Iterator` and instead
generalizes it to `Iterator for &mut I` where `I: Iterator + ?Sized`. The
`Box<I>` implementations were also updated.
The extra check caused by the expect() call can, in general, not be
optimized away, because the length of the iterator is unknown at compile
time, causing a noticable slow-down. Since the check only triggers if
the element isn't actually found in the iterator, i.e. it isn't
guaranteed to trigger for ill-behaved ExactSizeIterators, it seems
reasonable to switch to an implementation that doesn't need the check
and just always returns None if the value isn't found.
Benchmark:
````rust
let v: Vec<u8> = (0..1024*65).map(|_| 0).collect();
b.iter(|| {
v.as_slice().iter().rposition(|&c| c == 1)
});
````
Before:
````
test rposition ... bench: 49939 ns/iter (+/- 23)
````
After:
````
test rposition ... bench: 33306 ns/iter (+/- 68)
````
This removes the `ByRef` iterator adaptor to stay in line with the changes to
`std::io`. The `by_ref` method instead just returns `&mut Self`.
This also removes the implementation of `Iterator for &mut Iterator` and instead
generalizes it to `Iterator for &mut I` where `I: Iterator + ?Sized`. The
`Box<I>` implementations were also updated.
This is a breaking change due to the removal of the `std::iter::ByRef` type. All
mentions of `ByRef<'a, T>` should be replaced with `&mut T` to migrate forward.
[breaking-change]
The extra check caused by the expect() call can, in general, not be
optimized away, because the length of the iterator is unknown at compile
time, causing a noticable slow-down. Since the check only triggers if
the element isn't actually found in the iterator, i.e. it isn't
guaranteed to trigger for ill-behaved ExactSizeIterators, it seems
reasonable to switch to an implementation that doesn't need the check
and just always returns None if the value isn't found.
Benchmark:
````rust
let v: Vec<u8> = (0..1024*65).map(|_| 0).collect();
b.iter(|| {
v.as_slice().iter().rposition(|&c| c == 1)
});
````
Before:
````
test rposition ... bench: 49939 ns/iter (+/- 23)
````
After:
````
test rposition ... bench: 33306 ns/iter (+/- 68)
````
Now that associated types are fully implemented the iterator adaptors only need
type parameters which are associated with actual storage. All other type
parameters can either be derived from these (e.g. they are an associated type)
or can be bare on the `impl` block itself.
This is a breaking change due to the removal of type parameters on these
iterator adaptors, but code can fairly easily migrate by just deleting the
relevant type parameters for each adaptor. Other behavior should not be
affected.
Closes#21839
[breaking-change]
Now that associated types are fully implemented the iterator adaptors only need
type parameters which are associated with actual storage. All other type
parameters can either be derived from these (e.g. they are an associated type)
or can be bare on the `impl` block itself.
This is a breaking change due to the removal of type parameters on these
iterator adaptors, but code can fairly easily migrate by just deleting the
relevant type parameters for each adaptor. Other behavior should not be
affected.
Closes#21839
[breaking-change]
The new `::ops::Range` has separated implementations for each of the
numeric types, while the old `::iter::Range` has one for type `Int`.
However, we do not take output bindings into account when selecting
traits. So it confuses `typeck` and makes the new range does not work as
good as the old one when it comes to type inference.
This patch implements `Iterator` for the new range for one type `Int`.
This limitation could be lifted, however, if we ever reconsider the
output types' role in type inference.
Closes#21595Closes#21649Closes#21672
The new `::ops::Range` has separated implementations for each of the
numeric types, while the old `::iter::Range` has one for type `Int`.
However, we do not take output bindings into account when selecting
traits. So it confuses `typeck` and makes the new range does not work as
good as the old one when it comes to type inference.
This patch implements `Iterator` for the new range for one type `Int`.
This limitation could be lifted, however, if we ever reconsider the
output types' role in type inference.
Closes#21595Closes#21649Closes#21672
This commit marks as `#[stable]`:
* The `Index` and `IndexMut` traits. These are stabilized as taking the
index itself *by reference*; after extensive discussion it was
determined that this is a better match with our choices
elsewhere (e.g. making comparison operators auto-reference), and that
the use cases for by-value indices are better handled through
`IndexSet`.
* The `Range`, `RangeFrom` and `RangeTo` structs, introduced for range
notation.
* Various impls of `Index` and `IndexMut`.
The `FullRange` struct is left unstable as we may wish to rename it to
`RangeFull` in the future.
This commit also *removes* the `Step` trait in favor of direct
implementation of iterator traits on ranges for integers. The `Step`
trait was not a terribly useful factoring internally, and it is likely
that external integer types are best off implementing range iterators
directly. It was removed to simplify the API surface. We can always
reintroduce `Step` later if it turns out to be useful.
Due to this removal, this is a:
[breaking-change]
