Struct std::ptr::Shared

pub struct Shared<T> where T: ?Sized {
    // some fields omitted
}

Unstable (shared #27730)

: 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

unsafe fn new(ptr: *mut T) -> Shared<T>

Unstable (shared #27730)

Creates a new Shared.

Safety

ptr must be non-null.

Methods from Deref<Target=*mut T>

fn is_null(self) -> bool

Returns true if the pointer is null.

Examples

Basic usage:

fn main() { let mut s = [1, 2, 3]; let ptr: *mut u32 = s.as_mut_ptr(); assert!(!ptr.is_null()); }

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>

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:

fn main() { 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); } } }

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

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:

fn main() { let mut s = [1, 2, 3]; let ptr: *mut u32 = s.as_mut_ptr(); unsafe { println!("{}", *ptr.offset(1)); println!("{}", *ptr.offset(2)); } }

let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();

unsafe {
    println!("{}", *ptr.offset(1));
    println!("{}", *ptr.offset(2));
}

unsafe fn as_mut(self) -> Option<&'a mut T>

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:

fn main() { let mut s = [1, 2, 3]; let ptr: *mut u32 = s.as_mut_ptr(); }

let mut s = [1, 2, 3];
let ptr: *mut u32 = s.as_mut_ptr();

fn is_null(self) -> bool

Returns true if the pointer is null.

Examples

Basic usage:

fn main() { let s: &str = "Follow the rabbit"; let ptr: *const u8 = s.as_ptr(); assert!(!ptr.is_null()); }

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>

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:

fn main() { 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); } } }

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

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:

fn main() { let s: &str = "123"; let ptr: *const u8 = s.as_ptr(); unsafe { println!("{}", *ptr.offset(1) as char); println!("{}", *ptr.offset(2) as char); } }

let s: &str = "123";
let ptr: *const u8 = s.as_ptr();

unsafe {
    println!("{}", *ptr.offset(1) as char);
    println!("{}", *ptr.offset(2) as char);
}

Trait Implementations

impl<T> Pointer for Shared<T>

fn fmt(&self, f: &mut Formatter) -> Result<(), Error>

Unstable (shared #27730)

impl<T> Deref for Shared<T> where T: ?Sized

type Target = *mut T

Unstable (shared #27730)

fn deref(&self) -> &*mut T

Unstable (shared #27730)

impl<T, U> CoerceUnsized<Shared<U>> for Shared<T> where U: ?Sized, T: Unsize<U> + ?Sized

impl<T> Copy for Shared<T> where T: ?Sized

impl<T> Clone for Shared<T> where T: ?Sized

fn clone(&self) -> Shared<T>

Unstable (shared #27730)

fn clone_from(&mut self, source: &Self)

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: RefUnwindSafe + ?Sized> UnwindSafe for Shared<T>