This change has two consequences:
1. It makes `Arc<T>` and `Rc<T>` covariant in `T`.
2. It causes the compiler to reject code that was unsound with respect
to dropck. See compile-fail/issue-29106.rs for an example of code that
no longer compiles. Because of this, this is a [breaking-change].
Fixes#29037.
Fixes#29106.
These common traits were left off originally by accident from these smart
pointers, and a past attempt (#26008) to add them was later reverted (#26160)
due to unexpected breakge (#26096) occurring. The specific breakage in worry is
the meaning of this return value changed:
let a: Box<Option<T>> = ...;
a.as_ref()
Currently this returns `Option<&T>` but after this change it will return
`&Option<T>` because the `AsRef::as_ref` method shares the same name as
`Option::as_ref`. A [crater report][crater] of this change, however, has shown
that the fallout of this change is quite minimal. These trait implementations
are "the right impls to add" to these smart pointers and would enable various
generalizations such as those in #27197.
[crater]: https://gist.github.com/anonymous/0ba4c3512b07641c0f99
This commit is a breaking change for the above reasons mentioned, and the
mitigation strategies look like any of:
Option::as_ref(&a)
a.as_ref().as_ref()
(*a).as_ref()
* Add `Rc::would_unwrap(&Self) -> bool` to introspect whether try_unwrap would succeed,
because it's destructive (unlike get_mut).
* Move `rc.downgrade()` to `Rc::downgrade(&Self)` per conventions.
* Deprecate `Rc::weak_count` and `Rc::strong_count` for questionable utility.
* Deprecate `Rc::is_unique` for questionable semantics (there are two kinds of
uniqueness with Weak pointers in play).
* Rename `rc.make_unique()` to `Rc::make_mut(&mut Self)` per conventions, to
avoid uniqueness terminology, and to clarify the relation to `Rc::get_mut`.
This commit removes all unstable and deprecated functions in the standard
library. A release was recently cut (1.3) which makes this a good time for some
spring cleaning of the deprecated functions.
This commit is an implementation of [RFC 1184][rfc] which tweaks the behavior of
the `#![no_std]` attribute and adds a new `#![no_core]` attribute. The
`#![no_std]` attribute now injects `extern crate core` at the top of the crate
as well as the libcore prelude into all modules (in the same manner as the
standard library's prelude). The `#![no_core]` attribute disables both std and
core injection.
[rfc]: https://github.com/rust-lang/rfcs/pull/1184
This removes a footgun, since it is a reasonable assumption to make that
pointers to `T` will be aligned to `align_of::<T>()`. This also matches
the behaviour of C/C++. `min_align_of` is now deprecated.
Closes#21611.
This commit moves the free functions in the `rc`, `arc`, and `boxed` modules to
associated functions on their respective types, following the recent trend
towards this pattern. The previous free functions are all left in-place with
`#[deprecated]` pointers towards the new locations.
This commit also deprecates `arc::get_mut` and `Arc::make_unique` with no
replacement as they are racy in the face of weak pointers.
Use stable code in doc examples (libcollections)
Main task is to change from String::from_str to String::from in examples for String
(the latter constructor is stable). While I'm at it, also remove redundant feature flags,
fix some other instances of unstable code in examples (in examples for stable
methods), and remove some use of usize in examples too.
Prefer String::from over from_str; String::from_str is unstable while
String::from is stable. Promote the latter by using it in examples.
Simply migrating unstable function to the closest alternative.
* segfault due to not copying drop flag when coercing
* fat pointer casts
* segfault due to not checking drop flag properly
* debuginfo for DST smart pointers
* unreachable code in drop glue
Refactored code so that the drop-flag values for initialized
(`DTOR_NEEDED`) versus dropped (`DTOR_DONE`) are given explicit names.
Add `mem::dropped()` (which with `DTOR_DONE == 0` is semantically the
same as `mem::zeroed`, but the point is that it abstracts away from
the particular choice of value for `DTOR_DONE`).
Filling-drop needs to use something other than `ptr::read_and_zero`,
so I added such a function: `ptr::read_and_drop`. But, libraries
should not use it if they can otherwise avoid it.
Fixes to tests to accommodate filling-drop.
Alexis Beingessner