diff --git a/library/core/src/ptr/const_ptr.rs b/library/core/src/ptr/const_ptr.rs index ed16c5f051f7b..298a26ef58804 100644 --- a/library/core/src/ptr/const_ptr.rs +++ b/library/core/src/ptr/const_ptr.rs @@ -568,6 +568,31 @@ impl *const T { /// /// For non-`Sized` pointees this operation changes only the data pointer, /// leaving the metadata untouched. + /// + /// ## Examples + /// + /// ``` + /// #![feature(ptr_mask, strict_provenance)] + /// let v = 17_u32; + /// let ptr: *const u32 = &v; + /// + /// // `u32` is 4 bytes aligned, + /// // which means that lower 2 bits are always 0. + /// let tag_mask = 0b11; + /// let ptr_mask = !tag_mask; + /// + /// // We can store something in these lower bits + /// let tagged_ptr = ptr.map_addr(|a| a | 0b10); + /// + /// // Get the "tag" back + /// let tag = tagged_ptr.addr() & tag_mask; + /// assert_eq!(tag, 0b10); + /// + /// // Note that `tagged_ptr` is unaligned, it's UB to read from it. + /// // To get original pointer `mask` can be used: + /// let masked_ptr = tagged_ptr.mask(ptr_mask); + /// assert_eq!(unsafe { *masked_ptr }, 17); + /// ``` #[unstable(feature = "ptr_mask", issue = "98290")] #[must_use = "returns a new pointer rather than modifying its argument"] #[inline(always)] diff --git a/library/core/src/ptr/mut_ptr.rs b/library/core/src/ptr/mut_ptr.rs index 6764002bcd434..f71696e9ca0fa 100644 --- a/library/core/src/ptr/mut_ptr.rs +++ b/library/core/src/ptr/mut_ptr.rs @@ -588,6 +588,34 @@ impl *mut T { /// /// For non-`Sized` pointees this operation changes only the data pointer, /// leaving the metadata untouched. + /// + /// ## Examples + /// + /// ``` + /// #![feature(ptr_mask, strict_provenance)] + /// let mut v = 17_u32; + /// let ptr: *mut u32 = &mut v; + /// + /// // `u32` is 4 bytes aligned, + /// // which means that lower 2 bits are always 0. + /// let tag_mask = 0b11; + /// let ptr_mask = !tag_mask; + /// + /// // We can store something in these lower bits + /// let tagged_ptr = ptr.map_addr(|a| a | 0b10); + /// + /// // Get the "tag" back + /// let tag = tagged_ptr.addr() & tag_mask; + /// assert_eq!(tag, 0b10); + /// + /// // Note that `tagged_ptr` is unaligned, it's UB to read from/write to it. + /// // To get original pointer `mask` can be used: + /// let masked_ptr = tagged_ptr.mask(ptr_mask); + /// assert_eq!(unsafe { *masked_ptr }, 17); + /// + /// unsafe { *masked_ptr = 0 }; + /// assert_eq!(v, 0); + /// ``` #[unstable(feature = "ptr_mask", issue = "98290")] #[must_use = "returns a new pointer rather than modifying its argument"] #[inline(always)]