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pull/180/head
Joshua Nelson 5 years ago
parent 3e6e1001dc
commit e0702e4b9a
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@ -20,7 +20,7 @@ information that "completes" them (more on this below).
There are two major DSTs exposed by the language: There are two major DSTs exposed by the language:
* trait objects: `dyn MyTrait` * trait objects: `dyn MyTrait`
* slices: `[T]`, `str`, and others * slices: [`[T]`], [`str`], and others
A trait object represents some type that implements the traits it specifies. A trait object represents some type that implements the traits it specifies.
The exact original type is *erased* in favor of runtime reflection The exact original type is *erased* in favor of runtime reflection
@ -194,3 +194,5 @@ should behave.
[dst-issue]: https://github.com/rust-lang/rust/issues/26403 [dst-issue]: https://github.com/rust-lang/rust/issues/26403
[extern-types]: https://github.com/rust-lang/rfcs/blob/master/text/1861-extern-types.md [extern-types]: https://github.com/rust-lang/rfcs/blob/master/text/1861-extern-types.md
[`str`]: ../std/primitive.str.html
[`[T]`]: ../std/primitive.slice.html

@ -24,19 +24,19 @@ maintains the contracts the trait requires.
You can use `unsafe` on a block to declare that all unsafe actions performed You can use `unsafe` on a block to declare that all unsafe actions performed
within are verified to uphold the contracts of those operations. For instance, within are verified to uphold the contracts of those operations. For instance,
the index passed to `slice::get_unchecked` is in-bounds. the index passed to [`slice::get_unchecked`][get_unchecked] is in-bounds.
You can use `unsafe` on a trait implementation to declare that the implementation You can use `unsafe` on a trait implementation to declare that the implementation
upholds the trait's contract. For instance, that a type implementing `Send` is upholds the trait's contract. For instance, that a type implementing [`Send`] is
really safe to move to another thread. really safe to move to another thread.
The standard library has a number of unsafe functions, including: The standard library has a number of unsafe functions, including:
* `slice::get_unchecked`, which performs unchecked indexing, allowing * [`slice::get_unchecked`][get_unchecked], which performs unchecked indexing,
memory safety to be freely violated. allowing memory safety to be freely violated.
* `mem::transmute` reinterprets some value as having a given type, bypassing * [`mem::transmute`][transmute] reinterprets some value as having a given type,
type safety in arbitrary ways (see [conversions] for details). bypassing type safety in arbitrary ways (see [conversions] for details).
* Every raw pointer to a sized type has an `offset` method that * Every raw pointer to a sized type has an [`offset`][ptr_offset] method that
invokes Undefined Behavior if the passed offset is not ["in bounds"][ptr_offset]. invokes Undefined Behavior if the passed offset is not ["in bounds"][ptr_offset].
* All FFI (Foreign Function Interface) functions are `unsafe` to call because the * All FFI (Foreign Function Interface) functions are `unsafe` to call because the
other language can do arbitrary operations that the Rust compiler can't check. other language can do arbitrary operations that the Rust compiler can't check.
@ -65,11 +65,11 @@ relationship between Safe and Unsafe Rust. Safe Rust inherently has to
trust that any Unsafe Rust it touches has been written correctly. trust that any Unsafe Rust it touches has been written correctly.
On the other hand, Unsafe Rust has to be very careful about trusting Safe Rust. On the other hand, Unsafe Rust has to be very careful about trusting Safe Rust.
As an example, Rust has the `PartialOrd` and `Ord` traits to differentiate As an example, Rust has the [`PartialOrd`] and [`Ord`] traits to differentiate
between types which can "just" be compared, and those that provide a "total" between types which can "just" be compared, and those that provide a "total"
ordering (which basically means that comparison behaves reasonably). ordering (which basically means that comparison behaves reasonably).
`BTreeMap` doesn't really make sense for partially-ordered types, and so it [`BTreeMap`] doesn't really make sense for partially-ordered types, and so it
requires that its keys implement `Ord`. However, `BTreeMap` has Unsafe Rust code requires that its keys implement `Ord`. However, `BTreeMap` has Unsafe Rust code
inside of its implementation. Because it would be unacceptable for a sloppy `Ord` inside of its implementation. Because it would be unacceptable for a sloppy `Ord`
implementation (which is Safe to write) to cause Undefined Behavior, the Unsafe implementation (which is Safe to write) to cause Undefined Behavior, the Unsafe
@ -156,4 +156,8 @@ of the sort of care that must be taken, and what contracts Unsafe Rust must upho
[`GlobalAlloc`]: ../std/alloc/trait.GlobalAlloc.html [`GlobalAlloc`]: ../std/alloc/trait.GlobalAlloc.html
[conversions]: conversions.html [conversions]: conversions.html
[ptr_offset]: ../std/primitive.pointer.html#method.offset [ptr_offset]: ../std/primitive.pointer.html#method.offset
[get_unchecked]: ../std/primitive.slice.html#method.get_unchecked
[transmute]: ../std/mem/fn.transmute.html
[`PartialOrd`]: ../std/cmp/trait.PartialOrd.html
[`Ord`]: ../std/cmp/trait.Ord.html
[`BTreeMap`]: ../std/collections/struct.BTreeMap.html

@ -39,7 +39,7 @@ language cares about is preventing the following things:
(i.e., it must not be read from uninitialized memory) (i.e., it must not be read from uninitialized memory)
* a `str` that isn't valid UTF-8 * a `str` that isn't valid UTF-8
* a type with custom invalid values that is one of those values, such as a * a type with custom invalid values that is one of those values, such as a
`NonNull` that is null. (Requesting custom invalid values is an unstable [`NonNull`] that is null. (Requesting custom invalid values is an unstable
feature, but some stable libstd types, like `NonNull`, make use of it.) feature, but some stable libstd types, like `NonNull`, make use of it.)
"Producing" a value happens any time a value is assigned, passed to a "Producing" a value happens any time a value is assigned, passed to a
@ -85,3 +85,4 @@ these problems are considered impractical to categorically prevent.
[uninitialized memory]: uninitialized.html [uninitialized memory]: uninitialized.html
[race]: races.html [race]: races.html
[target features]: ../reference/attributes/codegen.html#the-target_feature-attribute [target features]: ../reference/attributes/codegen.html#the-target_feature-attribute
[`NonNull`]: ../std/ptr/struct.NonNull.html

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