Struct ethcore_util::standard::ptr::Shared
[−]
[src]
pub struct Shared<T> where T: ?Sized { /* fields omitted */ }
shared
): needs an RFC to flesh out design
A wrapper around a raw non-null *mut T
that indicates that the possessor
of this wrapper has shared ownership of the referent. Useful for
building abstractions like Rc<T>
or Arc<T>
, which internally
use raw pointers to manage the memory that they own.
Methods
impl<T> Shared<T> where T: ?Sized
Methods from Deref<Target=*mut T>
fn is_null(self) -> bool
1.0.0
Returns true if the pointer is null.
Examples
Basic usage:
let s: &str = "Follow the rabbit"; let ptr: *const u8 = s.as_ptr(); assert!(!ptr.is_null());
unsafe fn as_ref(self) -> Option<&'a T>
1.9.0
Returns None
if the pointer is null, or else returns a reference to
the value wrapped in Some
.
Safety
While this method and its mutable counterpart are useful for null-safety, it is important to note that this is still an unsafe operation because the returned value could be pointing to invalid memory.
Additionally, the lifetime 'a
returned is arbitrarily chosen and does
not necessarily reflect the actual lifetime of the data.
Examples
Basic usage:
let val: *const u8 = &10u8 as *const u8; unsafe { if let Some(val_back) = val.as_ref() { println!("We got back the value: {}!", val_back); } }
unsafe fn offset(self, count: isize) -> *const T
1.0.0
Calculates the offset from a pointer. count
is in units of T; e.g. a
count
of 3 represents a pointer offset of 3 * sizeof::<T>()
bytes.
Safety
Both the starting and resulting pointer must be either in bounds or one byte past the end of an allocated object. If either pointer is out of bounds or arithmetic overflow occurs then any further use of the returned value will result in undefined behavior.
Examples
Basic usage:
let s: &str = "123"; let ptr: *const u8 = s.as_ptr(); unsafe { println!("{}", *ptr.offset(1) as char); println!("{}", *ptr.offset(2) as char); }
fn wrapping_offset(self, count: isize) -> *const T
ptr_wrapping_offset
)Calculates the offset from a pointer using wrapping arithmetic.
count
is in units of T; e.g. a count
of 3 represents a pointer
offset of 3 * sizeof::<T>()
bytes.
Safety
The resulting pointer does not need to be in bounds, but it is
potentially hazardous to dereference (which requires unsafe
).
Always use .offset(count)
instead when possible, because offset
allows the compiler to optimize better.
Examples
Basic usage:
#![feature(ptr_wrapping_offset)] // Iterate using a raw pointer in increments of two elements let data = [1u8, 2, 3, 4, 5]; let mut ptr: *const u8 = data.as_ptr(); let step = 2; let end_rounded_up = ptr.wrapping_offset(6); // This loop prints "1, 3, 5, " while ptr != end_rounded_up { unsafe { print!("{}, ", *ptr); } ptr = ptr.wrapping_offset(step); }
fn is_null(self) -> bool
1.0.0
Returns true if the pointer is null.
Examples
Basic usage:
let mut s = [1, 2, 3]; let ptr: *mut u32 = s.as_mut_ptr(); assert!(!ptr.is_null());
unsafe fn as_ref(self) -> Option<&'a T>
1.9.0
Returns None
if the pointer is null, or else returns a reference to
the value wrapped in Some
.
Safety
While this method and its mutable counterpart are useful for null-safety, it is important to note that this is still an unsafe operation because the returned value could be pointing to invalid memory.
Additionally, the lifetime 'a
returned is arbitrarily chosen and does
not necessarily reflect the actual lifetime of the data.
Examples
Basic usage:
let val: *mut u8 = &mut 10u8 as *mut u8; unsafe { if let Some(val_back) = val.as_ref() { println!("We got back the value: {}!", val_back); } }
unsafe fn offset(self, count: isize) -> *mut T
1.0.0
Calculates the offset from a pointer. count
is in units of T; e.g. a
count
of 3 represents a pointer offset of 3 * sizeof::<T>()
bytes.
Safety
The offset must be in-bounds of the object, or one-byte-past-the-end.
Otherwise offset
invokes Undefined Behavior, regardless of whether
the pointer is used.
Examples
Basic usage:
let mut s = [1, 2, 3]; let ptr: *mut u32 = s.as_mut_ptr(); unsafe { println!("{}", *ptr.offset(1)); println!("{}", *ptr.offset(2)); }
fn wrapping_offset(self, count: isize) -> *mut T
ptr_wrapping_offset
)Calculates the offset from a pointer using wrapping arithmetic.
count
is in units of T; e.g. a count
of 3 represents a pointer
offset of 3 * sizeof::<T>()
bytes.
Safety
The resulting pointer does not need to be in bounds, but it is
potentially hazardous to dereference (which requires unsafe
).
Always use .offset(count)
instead when possible, because offset
allows the compiler to optimize better.
Examples
Basic usage:
#![feature(ptr_wrapping_offset)] // Iterate using a raw pointer in increments of two elements let mut data = [1u8, 2, 3, 4, 5]; let mut ptr: *mut u8 = data.as_mut_ptr(); let step = 2; let end_rounded_up = ptr.wrapping_offset(6); while ptr != end_rounded_up { unsafe { *ptr = 0; } ptr = ptr.wrapping_offset(step); } assert_eq!(&data, &[0, 2, 0, 4, 0]);
unsafe fn as_mut(self) -> Option<&'a mut T>
1.9.0
Returns None
if the pointer is null, or else returns a mutable
reference to the value wrapped in Some
.
Safety
As with as_ref
, this is unsafe because it cannot verify the validity
of the returned pointer, nor can it ensure that the lifetime 'a
returned is indeed a valid lifetime for the contained data.
Examples
Basic usage:
let mut s = [1, 2, 3]; let ptr: *mut u32 = s.as_mut_ptr(); let first_value = unsafe { ptr.as_mut().unwrap() }; *first_value = 4; println!("{:?}", s); // It'll print: "[4, 2, 3]".
Trait Implementations
impl<T, U> CoerceUnsized<Shared<U>> for Shared<T> where T: Unsize<U> + ?Sized, U: ?Sized
impl<T> !Sync for Shared<T> where T: ?Sized
Shared
pointers are not Sync
because the data they reference may be aliased.
impl<T> !Send for Shared<T> where T: ?Sized
Shared
pointers are not Send
because the data they reference may be aliased.
impl<T> Copy for Shared<T> where T: ?Sized
impl<T> Clone for Shared<T> where T: ?Sized
fn clone(&self) -> Shared<T>
Returns a copy of the value. Read more
fn clone_from(&mut self, source: &Self)
1.0.0
Performs copy-assignment from source
. Read more
impl<T> Pointer for Shared<T>
impl<T> Deref for Shared<T> where T: ?Sized
type Target = *mut T
The resulting type after dereferencing
fn deref(&self) -> &*mut T
The method called to dereference a value