bjoernager/rust
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rearrange for clarity

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This commit is contained in:
Ralf Jung 2018-09-17 15:21:20 +02:00
parent 2713d36679
commit 0ec87d0c92
1 changed files with 40 additions and 41 deletions
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81
src/libcore/ptr.rs
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@ -472,47 +472,6 @@ pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
///
/// Note that even if `T` has size `0`, the pointer must be non-NULL and properly aligned.
///
/// ## Ownership of the Returned Value
///
/// `read` creates a bitwise copy of `T`, regardless of whether `T` is [`Copy`].
/// If `T` is not [`Copy`], using both the returned value and the value at
/// `*src` can violate memory safety. Note that assigning to `src` counts as a
/// use because it will attempt to drop the value at `*src`.
///
/// [`write`] can be used to overwrite data without causing it to be dropped.
///
/// [valid]: ../ptr/index.html#safety
/// [`Copy`]: ../marker/trait.Copy.html
/// [`read_unaligned`]: ./fn.read_unaligned.html
/// [`write`]: ./fn.write.html
///
/// ```
/// use std::ptr;
///
/// let mut s = String::from("foo");
/// unsafe {
/// // `s2` now points to the same underlying memory as `s`.
/// let mut s2: String = ptr::read(&s);
///
/// assert_eq!(s2, "foo");
///
/// // Assigning to `s2` causes its original value to be dropped. Beyond
/// // this point, `s` must no longer be used, as the underlying memory has
/// // been freed.
/// s2 = String::default();
/// assert_eq!(s2, "");
///
/// // Assigning to `s` would cause the old value to be dropped again,
/// // resulting in undefined behavior.
/// // s = String::from("bar"); // ERROR
///
/// // `ptr::write` can be used to overwrite a value without dropping it.
/// ptr::write(&mut s, String::from("bar"));
/// }
///
/// assert_eq!(s, "bar");
/// ```
///
/// # Examples
///
/// Basic usage:
@ -565,7 +524,47 @@ pub unsafe fn replace<T>(dst: *mut T, mut src: T) -> T {
/// assert_eq!(bar, "foo");
/// ```
///
/// ## Ownership of the Returned Value
///
/// `read` creates a bitwise copy of `T`, regardless of whether `T` is [`Copy`].
/// If `T` is not [`Copy`], using both the returned value and the value at
/// `*src` can violate memory safety. Note that assigning to `*src` counts as a
/// use because it will attempt to drop the value at `*src`.
///
/// [`write`] can be used to overwrite data without causing it to be dropped.
///
/// ```
/// use std::ptr;
///
/// let mut s = String::from("foo");
/// unsafe {
/// // `s2` now points to the same underlying memory as `s`.
/// let mut s2: String = ptr::read(&s);
///
/// assert_eq!(s2, "foo");
///
/// // Assigning to `s2` causes its original value to be dropped. Beyond
/// // this point, `s` must no longer be used, as the underlying memory has
/// // been freed.
/// s2 = String::default();
/// assert_eq!(s2, "");
///
/// // Assigning to `s` would cause the old value to be dropped again,
/// // resulting in undefined behavior.
/// // s = String::from("bar"); // ERROR
///
/// // `ptr::write` can be used to overwrite a value without dropping it.
/// ptr::write(&mut s, String::from("bar"));
/// }
///
/// assert_eq!(s, "bar");
/// ```
///
/// [`mem::swap`]: ../mem/fn.swap.html
/// [valid]: ../ptr/index.html#safety
/// [`Copy`]: ../marker/trait.Copy.html
/// [`read_unaligned`]: ./fn.read_unaligned.html
/// [`write`]: ./fn.write.html
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub unsafe fn read<T>(src: *const T) -> T {