as_ptr returns a read-only pointer
Add comments to `as_ptr` methods to warn that these are read-only pointers, and writing to them is UB.
[It was pointed out](https://internals.rust-lang.org/t/as-ptr-vs-as-mut-ptr/9940) that `CStr` does not even have an `as_mut_ptr`. I originally was going to add one, but there is no method at all that would mutate a `CStr`. Was that a deliberate choice or should I add an `as_mut_ptr` (similar to [what I did for `str`](https://github.com/rust-lang/rust/pull/58200))?
Add implementations of last in terms of next_back on a bunch of DoubleEndedIterators
Provided a `DoubleEndedIterator` has finite length, `Iterator::last` is equivalent to `DoubleEndedIterator::next_back`. But searching forwards through the iterator when it's unnecessary is obviously not good for performance. I ran into this on one of the collection iterators.
I tried adding appropriate overloads for a bunch of the iterator adapters like filter, map, etc, but I ran into a lot of type inference failures after doing so.
The other interesting case is what to do with `Repeat`. Do we consider it part of the contract that `Iterator::last` will loop forever on it? The docs do say that the iterator will be evaluated until it returns None. This is also relevant for the adapters, it's trivially easy to observe whether a `Map` adapter invoked its closure a zillion times or just once for the last element.
implement specialized nth_back() for Bytes, Fuse and Enumerate
Hi,
After my first PR has been successfully merged, here is my second pull request :-)
Also this PR contains some specializations for the problem discussed in #54054.
There are two big categories of changes in here
- Removing lifetimes from common traits that can essentially never user a lifetime from an input (particularly `Drop` & `Debug`)
- Forwarding impls that are only possible because the lifetime doesn't matter (like `impl<R: Read + ?Sized> Read for &mut R`)
I omitted things that seemed like they could be more controversial, like the handful of iterators that have a `Item: 'static` despite the iterator having a lifetime or the `PartialEq` implementations where the flipped one cannot elide the lifetime.
fix str mutating through a ptr derived from &self
Found by Miri: In `get_unchecked_mut` (also used by the checked variants internally) uses `str::as_ptr` to create a mutable reference, but `as_ptr` takes `&self`. This means the mutable references we return here got created from a shared reference, which violates the shared-references-are-read-only discipline!
For this by using a newly introduced `as_mut_ptr` instead.
Some confusion about split popped up at https://news.ycombinator.com/item?id=19080931 since the docs sorta sound like `&str`, `char` and closures are the only types that can be patterns.
cc @steveklabnik
Mark str::trim.* functions as #[must_use].
The functions return a reference to a new object and do not modify in-place
as the following code shows:
````
let s = String::from(" hello ");
s.trim();
assert_eq!(s, " hello ");
````
The new reference should be bound to a variable as now indicated by #[must_use].
The functions return a reference to a new object and do not modify in-place
as the following code shows:
````
let s = String::from(" hello ");
s.trim();
assert_eq!(s, " hello ");
````
The new reference should be bound to a variable as now indicated by #[must_use].
