f94d671bfa
This commit revisits the `cast` module in libcore and libstd, and scrutinizes
all functions inside of it. The result was to remove the `cast` module entirely,
folding all functionality into the `mem` module. Specifically, this is the fate
of each function in the `cast` module.
* transmute - This function was moved to `mem`, but it is now marked as
#[unstable]. This is due to planned changes to the `transmute`
function and how it can be invoked (see the #[unstable] comment).
For more information, see RFC 5 and #12898
* transmute_copy - This function was moved to `mem`, with clarification that is
is not an error to invoke it with T/U that are different
sizes, but rather that it is strongly discouraged. This
function is now #[stable]
* forget - This function was moved to `mem` and marked #[stable]
* bump_box_refcount - This function was removed due to the deprecation of
managed boxes as well as its questionable utility.
* transmute_mut - This function was previously deprecated, and removed as part
of this commit.
* transmute_mut_unsafe - This function doesn't serve much of a purpose when it
can be achieved with an `as` in safe code, so it was
removed.
* transmute_lifetime - This function was removed because it is likely a strong
indication that code is incorrect in the first place.
* transmute_mut_lifetime - This function was removed for the same reasons as
`transmute_lifetime`
* copy_lifetime - This function was moved to `mem`, but it is marked
`#[unstable]` now due to the likelihood of being removed in
the future if it is found to not be very useful.
* copy_mut_lifetime - This function was also moved to `mem`, but had the same
treatment as `copy_lifetime`.
* copy_lifetime_vec - This function was removed because it is not used today,
and its existence is not necessary with DST
(copy_lifetime will suffice).
In summary, the cast module was stripped down to these functions, and then the
functions were moved to the `mem` module.
transmute - #[unstable]
transmute_copy - #[stable]
forget - #[stable]
copy_lifetime - #[unstable]
copy_mut_lifetime - #[unstable]
[breaking-change]
71 lines
2.4 KiB
Rust
71 lines
2.4 KiB
Rust
// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Types dealing with unsafe actions.
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use kinds::marker;
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/// Unsafe type that wraps a type T and indicates unsafe interior operations on the
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/// wrapped type. Types with an `Unsafe<T>` field are considered to have an *unsafe
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/// interior*. The Unsafe type is the only legal way to obtain aliasable data that is
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/// considered mutable. In general, transmuting an &T type into an &mut T is considered
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/// undefined behavior.
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///
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/// Although it is possible to put an Unsafe<T> into static item, it is not permitted to
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/// take the address of the static item if the item is not declared as mutable. This rule
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/// exists because immutable static items are stored in read-only memory, and thus any
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/// attempt to mutate their interior can cause segfaults. Immutable static items containing
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/// Unsafe<T> instances are still useful as read-only initializers, however, so we do not
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/// forbid them altogether.
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///
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/// Types like `Cell` and `RefCell` use this type to wrap their internal data.
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///
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/// Unsafe doesn't opt-out from any kind, instead, types with an `Unsafe` interior
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/// are expected to opt-out from kinds themselves.
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///
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/// # Example:
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///
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/// ```rust
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/// use std::ty::Unsafe;
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/// use std::kinds::marker;
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///
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/// struct NotThreadSafe<T> {
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/// value: Unsafe<T>,
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/// marker1: marker::NoShare
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/// }
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/// ```
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///
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/// **NOTE:** Unsafe<T> fields are public to allow static initializers. It is not recommended
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/// to access its fields directly, `get` should be used instead.
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#[lang="unsafe"]
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pub struct Unsafe<T> {
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/// Wrapped value
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pub value: T,
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/// Invariance marker
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pub marker1: marker::InvariantType<T>
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}
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impl<T> Unsafe<T> {
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/// Static constructor
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pub fn new(value: T) -> Unsafe<T> {
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Unsafe{value: value, marker1: marker::InvariantType}
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}
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/// Gets a mutable pointer to the wrapped value
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#[inline]
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pub unsafe fn get(&self) -> *mut T { &self.value as *T as *mut T }
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/// Unwraps the value
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#[inline]
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pub unsafe fn unwrap(self) -> T { self.value }
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}
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