# Crate alloc [−] [src]

Unstable (`alloc` #27783)

: this library is unlikely to be stabilized in its current form or name

# The Rust core allocation library

This is the lowest level library through which allocation in Rust can be performed.

This library, like libcore, is not intended for general usage, but rather as a building block of other libraries. The types and interfaces in this library are reexported through the standard library, and should not be used through this library.

Currently, there are four major definitions in this library.

## Boxed values

The `Box` type is a smart pointer type. There can only be one owner of a `Box`, and the owner can decide to mutate the contents, which live on the heap.

This type can be sent among threads efficiently as the size of a `Box` value is the same as that of a pointer. Tree-like data structures are often built with boxes because each node often has only one owner, the parent.

## Reference counted pointers

The `Rc` type is a non-threadsafe reference-counted pointer type intended for sharing memory within a thread. An `Rc` pointer wraps a type, `T`, and only allows access to `&T`, a shared reference.

This type is useful when inherited mutability (such as using `Box`) is too constraining for an application, and is often paired with the `Cell` or `RefCell` types in order to allow mutation.

## Atomically reference counted pointers

The `Arc` type is the threadsafe equivalent of the `Rc` type. It provides all the same functionality of `Rc`, except it requires that the contained type `T` is shareable. Additionally, `Arc<T>` is itself sendable while `Rc<T>` is not.

This types allows for shared access to the contained data, and is often paired with synchronization primitives such as mutexes to allow mutation of shared resources.

## Heap interfaces

The `heap` module defines the low-level interface to the default global allocator. It is not compatible with the libc allocator API.

## Reexports

`pub use oom::oom;`

## Modules

arc | Thread-safe reference-counting pointers.
boxed | A pointer type for heap allocation.
rc | Single-threaded reference-counting pointers.
heap | [Unstable]
oom | [Unstable]
raw_vec | [Unstable]

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