docs: Add example to `Iterator::take` with `by_ref`
If you want to logically split an iterator after `n` items, you might first discover `take`. Before this change, you'd find that `take` consumes the iterator, and you'd probably be stuck. The answer involves `by_ref`, but that's hard to discover, especially since `by_ref` is a bit abstract and `Iterator` has many methods.
After this change, you'd see the example showing `take` along with `by_ref`, which allows you to continue using the rest of the iterator. `by_ref` had a good example involving `take` already, so this change just duplicates that existing example under `take`.
If you want to logically split an iterator after `n` items, you might first
discover `take`. Before this change, you'd find that `take` consumes the
iterator, and you'd probably be stuck. The answer involves `by_ref`, but that's
hard to discover, especially since `by_ref` is a bit abstract and `Iterator`
has many methods.
After this change, you'd see the example showing `take` along with `by_ref`,
which allows you to continue using the rest of the iterator. `by_ref` had a
good example involving `take` already, so this change just duplicates that
existing example under `take`.
Avoid cloning in `Cloned<I>` or copying in `Copied<I>` when elements are
only needed by reference or not at all. There is already some precedent
for this, given that `__iterator_get_unchecked` is implemented, which
can skip elements. The reduced clones are technically observable by a
user impl of `Clone`.
...by adding an optimized implementation of `try_fold` and `fold` as well as replacing some unnecessary `mem::replace` calls with `MaybeUninit` helper methods.
debug-assert that the size_hint is well-formed in `collect`
Closes#137919
In the hopes of helping to catch any future accidentally-incorrect rustc or stdlib iterators (like the ones #137908 accidentally found), this has `Iterator::collect` call `size_hint` and check its `low` doesn't exceed its `Some(high)`.
There's of course a bazillion more places this *could* be checked, but the hope is that this one is a good tradeoff of being likely to catch lots of things while having minimal maintenance cost (especially compared to putting it in *every* container's `from_iter`).
Remove `#[cfg(not(test))]` gates in `core`
These gates are unnecessary now that unit tests for `core` are in a separate package, `coretests`, instead of in the same files as the source code. They previously prevented the two `core` versions from conflicting with each other.
library: Use `size_of` from the prelude instead of imported
Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the prelude instead of importing or qualifying them.
These functions were added to all preludes in Rust 1.80.
try-job: test-various
try-job: x86_64-gnu
try-job: x86_64-msvc-1
Use `std::mem::{size_of, size_of_val, align_of, align_of_val}` from the
prelude instead of importing or qualifying them.
These functions were added to all preludes in Rust 1.80.
These gates are unnecessary now that unit tests for `core` are in a
separate package, `coretests`, instead of in the same files as the
source code. They previously prevented the two `core` versions from
conflicting with each other.
Document workings of successors more clearly
This is an attempt to fix#135087 together with https://github.com/rust-lang/rust/pull/135886, but I am not sure if I've succeeded in adding much clarity here, so don't be shy with your comments.
Because the neutral element of `<fNN as iter::Sum>` was changed to
`neg_zero`, the documentation needed to be updated, as it was reporting
inadequate information about what should be expected from the return.
Co-authored-by: Jubilee <workingjubilee@gmail.com>
The implementation is unsound when a partially consumed iterator has
some elements buffered in the front/back parts and cloning the Iterator
removes the capacity from the backing vec::IntoIter.
Update Code Example for `Iterator::rposition`
Added an additional assertion to the example to show the behavior of `iter.next_back` after using `iter.rposition`.
