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Make align_of behave like min_align_of.

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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 is contained in:
Huon Wilson
2015-05-20 19:18:03 +10:00
parent 2ad26e850e
commit 225b116829
8 changed files with 47 additions and 53 deletions
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20
src/libcore/mem.rs
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@@ -155,6 +155,7 @@ pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[deprecated(reason = "use `align_of` instead", since = "1.1.0")]
pub fn min_align_of<T>() -> usize {
unsafe { intrinsics::min_align_of::<T>() }
}
@@ -170,14 +171,14 @@ pub fn min_align_of<T>() -> usize {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
#[deprecated(reason = "use `align_of_val` instead", since = "1.1.0")]
pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
unsafe { intrinsics::min_align_of_val(val) }
}
/// Returns the alignment in memory for a type.
///
/// This function will return the alignment, in bytes, of a type in memory. If the alignment
/// returned is adhered to, then the type is guaranteed to function properly.
/// This is the alignment used for struct fields. It may be smaller than the preferred alignment.
///
/// # Examples
///
@@ -189,17 +190,10 @@ pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn align_of<T>() -> usize {
// We use the preferred alignment as the default alignment for a type. This
// appears to be what clang migrated towards as well:
//
// http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20110725/044411.html
unsafe { intrinsics::pref_align_of::<T>() }
unsafe { intrinsics::min_align_of::<T>() }
}
/// Returns the alignment of the type of the value that `_val` points to.
///
/// This is similar to `align_of`, but function will properly handle types such as trait objects
/// (in the future), returning the alignment for an arbitrary value at runtime.
/// Returns the ABI-required minimum alignment of the type of the value that `val` points to
///
/// # Examples
///
@@ -210,8 +204,8 @@ pub fn align_of<T>() -> usize {
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn align_of_val<T>(_val: &T) -> usize {
align_of::<T>()
pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
unsafe { intrinsics::min_align_of_val(val) }
}
/// Creates a value initialized to zero.