bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

improve Vec example soundness in mem::transmute docs

Browse source
This commit is contained in:
Andre Bogus 2019-09-13 18:42:09 +02:00
parent 3287a65fc0
commit ab6e108644
1 changed files with 17 additions and 11 deletions
Download patch file Download diff file Expand all files Collapse all files

28
src/libcore/intrinsics.rs
View file

@ -845,21 +845,26 @@ extern "rust-intrinsic" {
///
/// ```
/// let store = [0, 1, 2, 3];
/// let mut v_orig = store.iter().collect::<Vec<&i32>>();
/// let v_orig = store.iter().collect::<Vec<&i32>>();
///
/// // clone the vector as we will reuse them later
/// let v_clone = v_orig.clone();
///
/// // Using transmute: this is Undefined Behavior, and a bad idea.
/// // However, it is no-copy.
/// let v_transmuted = unsafe {
/// std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(
/// v_orig.clone())
/// std::mem::transmute::<Vec<&i32>, Vec<Option<&i32>>>(v_clone)
/// };
///
/// let v_clone = v_orig.clone();
///
/// // This is the suggested, safe way.
/// // It does copy the entire vector, though, into a new array.
/// let v_collected = v_orig.clone()
/// .into_iter()
/// .map(|r| Some(r))
/// .collect::<Vec<Option<&i32>>>();
/// let v_collected = v_clone.into_iter()
/// .map(Some)
/// .collect::<Vec<Option<&i32>>>();
///
/// let v_clone = v_orig.clone();
///
/// // The no-copy, unsafe way, still using transmute, but not UB.
/// // This is equivalent to the original, but safer, and reuses the
@ -869,11 +874,12 @@ extern "rust-intrinsic" {
/// // the original inner type (`&i32`) to the converted inner type
/// // (`Option<&i32>`), so read the nomicon pages linked above.
/// let v_from_raw = unsafe {
/// Vec::from_raw_parts(v_orig.as_mut_ptr() as *mut Option<&i32>,
/// v_orig.len(),
/// v_orig.capacity())
/// // Ensure the original vector is not dropped.
/// let mut v_clone = std::mem::ManuallyDrop::new(v_clone);
/// Vec::from_raw_parts(v_clone.as_mut_ptr() as *mut Option<&i32>,
/// v_clone.len(),
/// v_clone.capacity())
/// };
/// std::mem::forget(v_orig);
/// ```
///
/// Implementing `split_at_mut`: