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Auto merge of #74940 - oli-obk:const_is_null, r=RalfJung

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Make `<*const T>::is_null` const fn

r? @RalfJung

cc @rust-lang/wg-const-eval

tracking issue: #74939
This commit is contained in:
bors 2020-08-17 14:13:13 +00:00
commit e8df0b8932
6 changed files with 204 additions and 7 deletions
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14
library/core/src/ptr/const_ptr.rs
View file

@ -13,6 +13,15 @@ impl<T: ?Sized> *const T {
/// Therefore, two pointers that are null may still not compare equal to
/// each other.
///
/// ## Behavior during const evaluation
///
/// When this function is used during const evaluation, it may return `false` for pointers
/// that turn out to be null at runtime. Specifically, when a pointer to some memory
/// is offset beyond its bounds in such a way that the resulting pointer is null,
/// the function will still return `false`. There is no way for CTFE to know
/// the absolute position of that memory, so we cannot tell if the pointer is
/// null or not.
///
/// # Examples
///
/// Basic usage:
@ -23,11 +32,12 @@ impl<T: ?Sized> *const T {
/// assert!(!ptr.is_null());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
#[inline]
pub fn is_null(self) -> bool {
pub const fn is_null(self) -> bool {
// Compare via a cast to a thin pointer, so fat pointers are only
// considering their "data" part for null-ness.
(self as *const u8) == null()
(self as *const u8).guaranteed_eq(null())
}
/// Casts to a pointer of another type.

14
library/core/src/ptr/mut_ptr.rs
View file

@ -12,6 +12,15 @@ impl<T: ?Sized> *mut T {
/// Therefore, two pointers that are null may still not compare equal to
/// each other.
///
/// ## Behavior during const evaluation
///
/// When this function is used during const evaluation, it may return `false` for pointers
/// that turn out to be null at runtime. Specifically, when a pointer to some memory
/// is offset beyond its bounds in such a way that the resulting pointer is null,
/// the function will still return `false`. There is no way for CTFE to know
/// the absolute position of that memory, so we cannot tell if the pointer is
/// null or not.
///
/// # Examples
///
/// Basic usage:
@ -22,11 +31,12 @@ impl<T: ?Sized> *mut T {
/// assert!(!ptr.is_null());
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
#[rustc_const_unstable(feature = "const_ptr_is_null", issue = "74939")]
#[inline]
pub fn is_null(self) -> bool {
pub const fn is_null(self) -> bool {
// Compare via a cast to a thin pointer, so fat pointers are only
// considering their "data" part for null-ness.
(self as *mut u8) == null_mut()
(self as *mut u8).guaranteed_eq(null_mut())
}
/// Casts to a pointer of another type.