Pointer types - The Rust Reference

# Pointer types

All pointers in Rust are explicit first-class values. They can be moved or copied, stored into data structs, and returned from functions.

## Shared references (`&`)

> Syntax
> ReferenceType :
> `&` Lifetime? `mut`? TypeNoBounds

These point to memory owned by some other value. When a shared reference to a value is created it prevents direct mutation of the value. Interior mutability provides an exception for this in certain circumstances. As the name suggests, any number of shared references to a value may exit. A shared reference type is written `&type`, or `&'a type` when you need to specify an explicit lifetime. Copying a reference is a "shallow" operation: it involves only copying the pointer itself, that is, pointers are `Copy`. Releasing a reference has no effect on the value it points to, but referencing of a temporary value will keep it alive during the scope of the reference itself.

## Mutable references (`&mut`)

These also point to memory owned by some other value. A mutable reference type is written `&mut type` or `&'a mut type`. A mutable reference (that hasn't been borrowed) is the only way to access the value it points to, so is not `Copy`.

## Raw pointers (`*const` and `*mut`)

> Syntax
> RawPointerType :
> `*` ( `mut` | `const` ) TypeNoBounds

Raw pointers are pointers without safety or liveness guarantees. Raw pointers are written as `*const T` or `*mut T`, for example `*const i32` means a raw pointer to a 32-bit integer. Copying or dropping a raw pointer has no effect on the lifecycle of any other value. Dereferencing a raw pointer is an `unsafe` operation, this can also be used to convert a raw pointer to a reference by reborrowing it (`&*` or `&mut *`). Raw pointers are generally discouraged in Rust code; they exist to support interoperability with foreign code, and writing performance-critical or low-level functions.

When comparing pointers they are compared by their address, rather than by what they point to. When comparing pointers to dynamically sized types they also have their addition data compared.

## Smart Pointers

The standard library contains additional 'smart pointer' types beyond references and raw pointers.