Struct std::ptr::Unique [] [src]

pub struct Unique<T> where T: ?Sized { /* fields omitted */ }
Unstable (unique #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 owns the referent. This in turn implies that the Unique<T> is Send/Sync if T is Send/Sync, unlike a raw *mut T (which conveys no particular ownership semantics). It also implies that the referent of the pointer should not be modified without a unique path to the Unique reference. Useful for building abstractions like Vec<T> or Box<T>, which internally use raw pointers to manage the memory that they own.

Methods

impl<T> Unique<T> where T: ?Sized
[src]

Unstable (unique #27730)

Creates a new Unique.

Safety

ptr must be non-null.

Unstable (unique #27730)

Dereferences the content.

Unstable (unique #27730)

Mutably dereferences the content.

Methods from Deref<Target=*mut T>

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());Run

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);
    }
}Run

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);
}Run

Unstable (ptr_wrapping_offset #37570)

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);
}Run

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());Run

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);
    }
}Run

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));
}Run

Unstable (ptr_wrapping_offset #37570)

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]);Run

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]".Run

Trait Implementations

impl<T> Deref for Unique<T> where T: ?Sized
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The resulting type after dereferencing

The method called to dereference a value

impl<T> Sync for Unique<T> where T: Sync + ?Sized
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Unique pointers are Sync if T is Sync because the data they reference is unaliased. Note that this aliasing invariant is unenforced by the type system; the abstraction using the Unique must enforce it.

impl<T> Pointer for Unique<T>
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Formats the value using the given formatter.

impl<T> Send for Unique<T> where T: Send + ?Sized
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Unique pointers are Send if T is Send because the data they reference is unaliased. Note that this aliasing invariant is unenforced by the type system; the abstraction using the Unique must enforce it.

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