The Rust Standard Library is the foundation of portable Rust software, a
set of minimal and battle-tested shared abstractions for the broader Rust
ecosystem. It offers core types, like
Option<T>, library-defined operations on language
primitives, standard macros, I/O and
multithreading, among many other things.
If you already know the name of what you are looking for, the fastest way to find it is to use the search bar at the top of the page.
Otherwise, you may want to jump to one of these useful sections:
If this is your first time, the documentation for the standard library is written to be casually perused. Clicking on interesting things should generally lead you to interesting places. Still, there are important bits you don’t want to miss, so read on for a tour of the standard library and its documentation!
Once you are familiar with the contents of the standard library you may
begin to find the verbosity of the prose distracting. At this stage in your
development you may want to press the
[-] button near the top of the
page to collapse it into a more skimmable view.
While you are looking at that
[-] button also notice the
link. Rust’s API documentation comes with the source code and you are
encouraged to read it. The standard library source is generally high
quality and a peek behind the curtains is often enlightening.
First of all, The Rust Standard Library is divided into a number of focused
modules, all listed further down this page. These modules are
the bedrock upon which all of Rust is forged, and they have mighty names
std::cmp. Modules’ documentation typically
includes an overview of the module along with examples, and are a smart
place to start familiarizing yourself with the library.
Second, implicit methods on primitive types are documented here. This can be a source of confusion for two reasons:
- While primitives are implemented by the compiler, the standard library implements methods directly on the primitive types (and it is the only library that does so), which are documented in the section on primitives.
- The standard library exports many modules with the same name as primitive types. These define additional items related to the primitive type, but not the all-important methods.
So for example there is a page for the primitive type
i32 that lists all the methods that can be called on
32-bit integers (very useful), and there is a page for the module
std::i32 that documents the constant values
Third, the standard library defines The Rust Prelude, a small collection of items - mostly traits - that are imported into every module of every crate. The traits in the prelude are pervasive, making the prelude documentation a good entry point to learning about the library.
And finally, the standard library exports a number of standard macros, and lists them on this page (technically, not all of the standard macros are defined by the standard library - some are defined by the compiler - but they are documented here the same). Like the prelude, the standard macros are imported by default into all crates.
Check out the rust contribution guidelines here. The source for this documentation can be found on GitHub. To contribute changes, make sure you read the guidelines first, then submit pull-requests for your suggested changes.
Contributions are appreciated! If you see a part of the docs that can be improved, submit a PR, or chat with us first on Discord #docs.
The rest of this crate documentation is dedicated to pointing out notable features of The Rust Standard Library.
result modules define optional and error-handling
Result<T, E>. The
iter module defines
Rust’s iterator trait,
Iterator, which works with the
for loop to
The standard library exposes three common ways to deal with contiguous regions of memory:
Vec<T>- A heap-allocated vector that is resizable at runtime.
[T; N]- An inline array with a fixed size at compile time.
[T]- A dynamically sized slice into any other kind of contiguous storage, whether heap-allocated or not.
Slices can only be handled through some kind of pointer, and as such come in many flavors such as:
&[T]- shared slice
&mut [T]- mutable slice
Box<[T]>- owned slice
str, a UTF-8 string slice, is a primitive type, and the standard library
defines many methods for it. Rust
strs are typically accessed as
&str. Use the owned
String for building and
Data may be shared by placing it in a reference-counted box or the
type, and if further contained in a
RefCell, may be mutated
as well as shared. Likewise, in a concurrent setting it is common to pair an
Arc, with a
Mutex to get the same
Besides basic data types, the standard library is largely concerned with abstracting over differences in common platforms, most notably Windows and Unix derivatives.
Many parts of the standard library are expected to work before and after
but this is not guaranteed or ensured by tests. It is recommended that you write your own tests
and run them on each platform you wish to support.
This means that use of
std before/after main, especially of features that interact with the
OS or global state, is exempted from stability and portability guarantees and instead only
provided on a best-effort basis. Nevertheless bug reports are appreciated.
On the other hand
alloc are most likely to work in such environments with
the caveat that any hookable behavior such as panics, oom handling or allocators will also
depend on the compatibility of the hooks.
Some features may also behave differently outside main, e.g. stdio could become unbuffered, some panics might turn into aborts, backtraces might not get symbolicated or similar.
Non-exhaustive list of known limitations:
!type, also called “never”.
- A fixed-size array, denoted
[T; N], for the element type,
T, and the non-negative compile-time constant size,
- The boolean type.
- A character type.
- A 32-bit floating point type (specifically, the “binary32” type defined in IEEE 754-2008).
- A 64-bit floating point type (specifically, the “binary64” type defined in IEEE 754-2008).
- Function pointers, like
fn(usize) -> bool.
- The 8-bit signed integer type.
- The 16-bit signed integer type.
- The 32-bit signed integer type.
- The 64-bit signed integer type.
- The 128-bit signed integer type.
- The pointer-sized signed integer type.
- Raw, unsafe pointers,
*const T, and
- A dynamically-sized view into a contiguous sequence,
[T]. Contiguous here means that elements are laid out so that every element is the same distance from its neighbors.
- String slices.
- A finite heterogeneous sequence,
(T, U, ..).
- The 8-bit unsigned integer type.
- The 16-bit unsigned integer type.
- The 32-bit unsigned integer type.
- The 64-bit unsigned integer type.
- The 128-bit unsigned integer type.
()type, also called “unit”.
- The pointer-sized unsigned integer type.
- assert_matchesExperimentalUnstable module containing the unstable
- async_iterExperimentalComposable asynchronous iteration.
- intrinsicsExperimentalCompiler intrinsics.
- simdExperimentalPortable SIMD module.
- Memory allocation APIs.
- Utilities for dynamic typing or type reflection.
- SIMD and vendor intrinsics module.
- Utilities for the array primitive type.
- Operations on ASCII strings and characters.
- Support for capturing a stack backtrace of an OS thread
- A module for working with borrowed data.
Box<T>type for heap allocation.
- Shareable mutable containers.
- Utilities for the
Clonetrait for types that cannot be ‘implicitly copied’.
- Utilities for comparing and ordering values.
- Collection types.
- Traits for conversions between types.
Defaulttrait for types with a default value.
- Inspection and manipulation of the process’s environment.
- Interfaces for working with Errors.
- Constants for the
f32single-precision floating point type.
- Constants for the
f64double-precision floating point type.
- Utilities related to FFI bindings.
- Utilities for formatting and printing
- Filesystem manipulation operations.
- Asynchronous basic functionality.
- Generic hashing support.
- Hints to compiler that affects how code should be emitted or optimized. Hints may be compile time or runtime.
- i8Deprecation plannedRedundant constants module for the
- i16Deprecation plannedRedundant constants module for the
- i32Deprecation plannedRedundant constants module for the
- i64Deprecation plannedRedundant constants module for the
- i128Deprecation plannedRedundant constants module for the
- Traits, helpers, and type definitions for core I/O functionality.
- isizeDeprecation plannedRedundant constants module for the
- Composable external iteration.
- Primitive traits and types representing basic properties of types.
- Basic functions for dealing with memory.
- Networking primitives for TCP/UDP communication.
- Additional functionality for numerics.
- Overloadable operators.
- Optional values.
- OS-specific functionality.
- Panic support in the standard library.
- Cross-platform path manipulation.
- Types that pin data to its location in memory.
- The Rust Prelude
- This module reexports the primitive types to allow usage that is not possibly shadowed by other declared types.
- A module for working with processes.
- Manually manage memory through raw pointers.
- Single-threaded reference-counting pointers. ‘Rc’ stands for ‘Reference Counted’.
- Error handling with the
- Utilities for the slice primitive type.
- Utilities for the
- A UTF-8–encoded, growable string.
- Useful synchronization primitives.
- Types and Traits for working with asynchronous tasks.
- Native threads.
- Temporal quantification.
- u8Deprecation plannedRedundant constants module for the
- u16Deprecation plannedRedundant constants module for the
- u32Deprecation plannedRedundant constants module for the
- u64Deprecation plannedRedundant constants module for the
- u128Deprecation plannedRedundant constants module for the
- usizeDeprecation plannedRedundant constants module for the
- A contiguous growable array type with heap-allocated contents, written
- cfg_matchExperimentalA macro for defining
- concat_bytesExperimentalConcatenates literals into a byte slice.
- concat_identsExperimentalConcatenates identifiers into one identifier.
- const_format_argsExperimentalSame as
format_args, but can be used in some const contexts.
- format_args_nlExperimentalSame as
format_args, but adds a newline in the end.
- log_syntaxExperimentalPrints passed tokens into the standard output.
- trace_macrosExperimentalEnables or disables tracing functionality used for debugging other macros.
- Asserts that a boolean expression is
- Asserts that two expressions are equal to each other (using
- Asserts that two expressions are not equal to each other (using
- Evaluates boolean combinations of configuration flags at compile-time.
- Expands to the column number at which it was invoked.
- Causes compilation to fail with the given error message when encountered.
- Concatenates literals into a static string slice.
- Prints and returns the value of a given expression for quick and dirty debugging.
- Asserts that a boolean expression is
- Asserts that two expressions are equal to each other.
- Asserts that two expressions are not equal to each other.
- Inspects an environment variable at compile time.
- Prints to the standard error.
- Prints to the standard error, with a newline.
- Expands to the file name in which it was invoked.
- Creates a
Stringusing interpolation of runtime expressions.
- Constructs parameters for the other string-formatting macros.
- Parses a file as an expression or an item according to the context.
- Includes a file as a reference to a byte array.
- Includes a UTF-8 encoded file as a string.
- is_x86_feature_detectedx86 or x86-64A macro to test at runtime whether a CPU feature is available on x86/x86-64 platforms.
- Expands to the line number on which it was invoked.
- Returns whether the given expression matches any of the given patterns.
- Expands to a string that represents the current module path.
- Optionally inspects an environment variable at compile time.
- Panics the current thread.
- Prints to the standard output.
- Prints to the standard output, with a newline.
- Stringifies its arguments.
- Declare a new thread local storage key of type
- Indicates unfinished code.
- tryDeprecatedUnwraps a result or propagates its error.
- Indicates unimplemented code by panicking with a message of “not implemented”.
- Indicates unreachable code.
- Creates a
Veccontaining the arguments.
- Writes formatted data into a buffer.
- Write formatted data into a buffer, with a newline appended.
- Cast between types, or rename an import.
- Return a
Futureinstead of blocking the current thread.
- Suspend execution until the result of a
- Exit early from a loop.
- Compile-time constants, compile-time evaluable functions, and raw pointers.
- Skip to the next iteration of a loop.
- A Rust binary or library.
dynis a prefix of a trait object’s type.
- A type that can be any one of several variants.
- Link to or import external code.
- A value of type
boolrepresenting logical false.
- A function or function pointer.
- Evaluate a block if a condition holds.
- Implement some functionality for a type.
- Iterate over a series of values with
- Bind a value to a variable.
- Loop indefinitely.
- Control flow based on pattern matching.
- Organize code into modules.
- Capture a closure’s environment by value.
- A mutable variable, reference, or pointer.
- Make an item visible to others.
- Bind by reference during pattern matching.
- Return a value from a function.
- The receiver of a method, or the current module.
- A static item is a value which is valid for the entire duration of your program (a
- A type that is composed of other types.
- The parent of the current module.
- A common interface for a group of types.
- A value of type
boolrepresenting logical true.
- Define an alias for an existing type.
- Code or interfaces whose memory safety cannot be verified by the type system.
- Import or rename items from other crates or modules.
- Add constraints that must be upheld to use an item.
- Loop while a condition is upheld.