1.0.0[][src]Crate std

The Rust Standard Library

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 Vec<T> and Option<T>, library-defined operations on language primitives, standard macros, I/O and multithreading, among many other things.

std is available to all Rust crates by default. Therefore, the standard library can be accessed in use statements through the path std, as in use std::env.

How to read this documentation

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 [src] button. 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.

What is in the standard library documentation?

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 like std::slice and 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:

  1. 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.
  2. 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 MIN and MAX (rarely useful).

Note the documentation for the primitives str and [T] (also called 'slice'). Many method calls on String and Vec<T> are actually calls to methods on str and [T] respectively, via deref coercions.

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.

Contributing changes to the documentation

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 irc.mozilla.org #rust-docs.

A Tour of The Rust Standard Library

The rest of this crate documentation is dedicated to pointing out notable features of The Rust Standard Library.

Containers and collections

The option and result modules define optional and error-handling types, Option<T> and Result<T, E>. The iter module defines Rust's iterator trait, Iterator, which works with the for loop to access collections.

The standard library exposes three common ways to deal with contiguous regions of memory:

Slices can only be handled through some kind of pointer, and as such come in many flavors such as:

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 immutable references: &str. Use the owned String for building and mutating strings.

For converting to strings use the format! macro, and for converting from strings use the FromStr trait.

Data may be shared by placing it in a reference-counted box or the Rc type, and if further contained in a Cell or RefCell, may be mutated as well as shared. Likewise, in a concurrent setting it is common to pair an atomically-reference-counted box, Arc, with a Mutex to get the same effect.

The collections module defines maps, sets, linked lists and other typical collection types, including the common HashMap<K, V>.

Platform abstractions and I/O

Besides basic data types, the standard library is largely concerned with abstracting over differences in common platforms, most notably Windows and Unix derivatives.

Common types of I/O, including files, TCP, UDP, are defined in the io, fs, and net modules.

The thread module contains Rust's threading abstractions. sync contains further primitive shared memory types, including atomic and mpsc, which contains the channel types for message passing.

Re-exports

pub use core::arch;

Primitive Types

array

A fixed-size array, denoted [T; N], for the element type, T, and the non-negative compile-time constant size, N.

bool

The boolean type.

char

A character type.

f32

The 32-bit floating point type.

f64

The 64-bit floating point type.

fn

Function pointers, like fn(usize) -> bool.

i8

The 8-bit signed integer type.

i16

The 16-bit signed integer type.

i32

The 32-bit signed integer type.

i64

The 64-bit signed integer type.

i128

The 128-bit signed integer type.

isize

The pointer-sized signed integer type.

pointer

Raw, unsafe pointers, *const T, and *mut T.

reference

References, both shared and mutable.

slice

A dynamically-sized view into a contiguous sequence, [T].

str

String slices.

tuple

A finite heterogeneous sequence, (T, U, ..).

u8

The 8-bit unsigned integer type.

u16

The 16-bit unsigned integer type.

u32

The 32-bit unsigned integer type.

u64

The 64-bit unsigned integer type.

u128

The 128-bit unsigned integer type.

unit

The () type, sometimes called "unit" or "nil".

usize

The pointer-sized unsigned integer type.

neverExperimental

The ! type, also called "never".

Modules

alloc

Memory allocation APIs

any

This module implements the Any trait, which enables dynamic typing of any 'static type through runtime reflection.

array

Implementations of things like Eq for fixed-length arrays up to a certain length. Eventually we should able to generalize to all lengths.

ascii

Operations on ASCII strings and characters.

borrow

A module for working with borrowed data.

boxed

A pointer type for heap allocation.

cell

Shareable mutable containers.

char

A character type.

clone

The Clone trait for types that cannot be 'implicitly copied'.

cmp

Functionality for ordering and comparison.

collections

Collection types.

convert

Traits for conversions between types.

default

The Default trait for types which may have meaningful default values.

env

Inspection and manipulation of the process's environment.

error

Traits for working with Errors.

f32

This module provides constants which are specific to the implementation of the f32 floating point data type.

f64

This module provides constants which are specific to the implementation of the f64 floating point data type.

ffi

Utilities related to FFI bindings.

fmt

Utilities for formatting and printing Strings.

fs

Filesystem manipulation operations.

future

Asynchronous values.

hash

Generic hashing support.

hint

Hints to compiler that affects how code should be emitted or optimized.

i8

The 8-bit signed integer type.

i16

The 16-bit signed integer type.

i32

The 32-bit signed integer type.

i64

The 64-bit signed integer type.

i128

The 128-bit signed integer type.

io

Traits, helpers, and type definitions for core I/O functionality.

isize

The pointer-sized signed integer type.

iter

Composable external iteration.

marker

Primitive traits and types representing basic properties of types.

mem

Basic functions for dealing with memory.

net

Networking primitives for TCP/UDP communication.

num

Additional functionality for numerics.

ops

Overloadable operators.

option

Optional values.

os

OS-specific functionality.

panic

Panic support in the standard library.

path

Cross-platform path manipulation.

pin

Types that pin data to its location in memory.

prelude

The Rust Prelude.

process

A module for working with processes.

ptr

Manually manage memory through raw pointers.

rc

Single-threaded reference-counting pointers. 'Rc' stands for 'Reference Counted'.

result

Error handling with the Result type.

slice

A dynamically-sized view into a contiguous sequence, [T].

str

Unicode string slices.

string

A UTF-8 encoded, growable string.

sync

Useful synchronization primitives.

task

Types and Traits for working with asynchronous tasks.

thread

Native threads.

time

Temporal quantification.

u8

The 8-bit unsigned integer type.

u16

The 16-bit unsigned integer type.

u32

The 32-bit unsigned integer type.

u64

The 64-bit unsigned integer type.

u128

The 128-bit unsigned integer type.

usize

The pointer-sized unsigned integer type.

vec

A contiguous growable array type with heap-allocated contents, written Vec<T>.

intrinsicsExperimental

Compiler intrinsics.

rawExperimental

Contains struct definitions for the layout of compiler built-in types.

Macros

assert

Asserts that a boolean expression is true at runtime.

assert_eq

Asserts that two expressions are equal to each other (using PartialEq).

assert_ne

Asserts that two expressions are not equal to each other (using PartialEq).

cfg

Evaluates boolean combinations of configuration flags at compile-time.

column

Expands to the column number at which it was invoked.

compile_error

Causes compilation to fail with the given error message when encountered.

concat

Concatenates literals into a static string slice.

dbg

Prints and returns the value of a given expression for quick and dirty debugging.

debug_assert

Asserts that a boolean expression is true at runtime.

debug_assert_eq

Asserts that two expressions are equal to each other.

debug_assert_ne

Asserts that two expressions are not equal to each other.

env

Inspects an environment variable at compile time.

eprint

Prints to the standard error.

eprintln

Prints to the standard error, with a newline.

file

Expands to the file name in which it was invoked.

format

Creates a String using interpolation of runtime expressions.

format_args

Constructs parameters for the other string-formatting macros.

include

Parses a file as an expression or an item according to the context.

include_bytes

Includes a file as a reference to a byte array.

include_str

Includes a utf8-encoded file as a string.

is_x86_feature_detected

A macro to test at runtime whether a CPU feature is available on x86/x86-64 platforms.

line

Expands to the line number on which it was invoked.

module_path

Expands to a string that represents the current module path.

option_env

Optionally inspects an environment variable at compile time.

panic

Panics the current thread.

print

Prints to the standard output.

println

Prints to the standard output, with a newline.

stringify

Stringifies its arguments.

thread_local

Declare a new thread local storage key of type std::thread::LocalKey.

tryDeprecation planned

Unwraps a result or propagates its error.

unimplemented

Indicates unfinished code.

unreachable

Indicates unreachable code.

vec

Creates a Vec containing the arguments.

write

Writes formatted data into a buffer.

writeln

Write formatted data into a buffer, with a newline appended.

__rust_unstable_columnExperimental

Same as column, but less likely to be shadowed.

asmExperimental

Inline assembly.

concat_identsExperimental

Concatenates identifiers into one identifier.

format_args_nlExperimental

Same as format_args, but adds a newline in the end.

global_asmExperimental

Module-level inline assembly.

is_aarch64_feature_detectedExperimental

Prevents compilation if is_aarch64_feature_detected is used somewhere else than aarch64 targets.

is_arm_feature_detectedExperimental

Prevents compilation if is_arm_feature_detected is used somewhere else than ARM targets.

is_mips64_feature_detectedExperimental

Prevents compilation if is_mips64_feature_detected is used somewhere else than MIPS64 targets.

is_mips_feature_detectedExperimental

Prevents compilation if is_mips_feature_detected is used somewhere else than MIPS targets.

is_powerpc64_feature_detectedExperimental

Prevents compilation if is_powerpc64_feature_detected is used somewhere else than PowerPC64 targets.

is_powerpc_feature_detectedExperimental

Prevents compilation if is_powerpc_feature_detected is used somewhere else than PowerPC targets.

log_syntaxExperimental

Prints passed tokens into the standard output.

todoExperimental

Indicates unfinished code.

trace_macrosExperimental

Enables or disables tracing functionality used for debugging other macros.

Keywords

Self

The implementing type within a trait or impl block, or the current type within a type definition.

as

Cast between types, or rename an import.

asyncExperimental

Return a Future instead of blocking the current thread.

awaitExperimental

Suspend execution until the result of a Future is ready.

break

Exit early from a loop.

const

Compile-time constants and deterministic functions.

continue

Skip to the next iteration of a loop.

crate

A Rust binary or library.

dyn

Name the type of a trait object.

else

What to do when an if condition does not hold.

enum

A type that can be any one of several variants.

extern

Link to or import external code.

false

A value of type bool representing logical false.

fn

A function or function pointer.

for

Iteration with in, trait implementation with impl, or higher-ranked trait bounds (for<'a>).

if

Evaluate a block if a condition holds.

impl

Implement some functionality for a type.

in

Iterate over a series of values with for.

let

Bind a value to a variable.

loop

Loop indefinitely.

match

Control flow based on pattern matching.

mod

Organize code into modules.

move

Capture a closure's environment by value.

mut

A mutable binding, reference, or pointer.

pub

Make an item visible to others.

ref

Bind by reference during pattern matching.

return

Return a value from a function.

self

The receiver of a method, or the current module.

static

A place that is valid for the duration of a program.

struct

A type that is composed of other types.

super

The parent of the current module.

trait

A common interface for a class of types.

true

A value of type bool representing logical true.

type

Define an alias for an existing type.

union

The Rust equivalent of a C-style union.

unsafe

Code or interfaces whose memory safety cannot be verified by the type system.

use

Import or rename items from other crates or modules.

where

Add constraints that must be upheld to use an item.

while

Loop while a condition is upheld.