1 //! # The Rust Standard Library
3 //! The Rust Standard Library is the foundation of portable Rust software, a
4 //! set of minimal and battle-tested shared abstractions for the [broader Rust
5 //! ecosystem][crates.io]. It offers core types, like [`Vec<T>`] and
6 //! [`Option<T>`], library-defined [operations on language
7 //! primitives](#primitives), [standard macros](#macros), [I/O] and
8 //! [multithreading], among [many other things][other].
10 //! `std` is available to all Rust crates by default. Therefore, the
11 //! standard library can be accessed in [`use`] statements through the path
12 //! `std`, as in [`use std::env`].
14 //! # How to read this documentation
16 //! If you already know the name of what you are looking for, the fastest way to
17 //! find it is to use the <a href="#" onclick="focusSearchBar();">search
18 //! bar</a> at the top of the page.
20 //! Otherwise, you may want to jump to one of these useful sections:
22 //! * [`std::*` modules](#modules)
23 //! * [Primitive types](#primitives)
24 //! * [Standard macros](#macros)
25 //! * [The Rust Prelude]
27 //! If this is your first time, the documentation for the standard library is
28 //! written to be casually perused. Clicking on interesting things should
29 //! generally lead you to interesting places. Still, there are important bits
30 //! you don't want to miss, so read on for a tour of the standard library and
31 //! its documentation!
33 //! Once you are familiar with the contents of the standard library you may
34 //! begin to find the verbosity of the prose distracting. At this stage in your
35 //! development you may want to press the `[-]` button near the top of the
36 //! page to collapse it into a more skimmable view.
38 //! While you are looking at that `[-]` button also notice the `[src]`
39 //! button. Rust's API documentation comes with the source code and you are
40 //! encouraged to read it. The standard library source is generally high
41 //! quality and a peek behind the curtains is often enlightening.
43 //! # What is in the standard library documentation?
45 //! First of all, The Rust Standard Library is divided into a number of focused
46 //! modules, [all listed further down this page](#modules). These modules are
47 //! the bedrock upon which all of Rust is forged, and they have mighty names
48 //! like [`std::slice`] and [`std::cmp`]. Modules' documentation typically
49 //! includes an overview of the module along with examples, and are a smart
50 //! place to start familiarizing yourself with the library.
52 //! Second, implicit methods on [primitive types] are documented here. This can
53 //! be a source of confusion for two reasons:
55 //! 1. While primitives are implemented by the compiler, the standard library
56 //! implements methods directly on the primitive types (and it is the only
57 //! library that does so), which are [documented in the section on
58 //! primitives](#primitives).
59 //! 2. The standard library exports many modules *with the same name as
60 //! primitive types*. These define additional items related to the primitive
61 //! type, but not the all-important methods.
63 //! So for example there is a [page for the primitive type
64 //! `i32`](primitive.i32.html) that lists all the methods that can be called on
65 //! 32-bit integers (very useful), and there is a [page for the module
66 //! `std::i32`] that documents the constant values [`MIN`] and [`MAX`] (rarely
69 //! Note the documentation for the primitives [`str`] and [`[T]`][slice] (also
70 //! called 'slice'). Many method calls on [`String`] and [`Vec<T>`] are actually
71 //! calls to methods on [`str`] and [`[T]`][slice] respectively, via [deref
72 //! coercions][deref-coercions].
74 //! Third, the standard library defines [The Rust Prelude], a small collection
75 //! of items - mostly traits - that are imported into every module of every
76 //! crate. The traits in the prelude are pervasive, making the prelude
77 //! documentation a good entry point to learning about the library.
79 //! And finally, the standard library exports a number of standard macros, and
80 //! [lists them on this page](#macros) (technically, not all of the standard
81 //! macros are defined by the standard library - some are defined by the
82 //! compiler - but they are documented here the same). Like the prelude, the
83 //! standard macros are imported by default into all crates.
85 //! # Contributing changes to the documentation
87 //! Check out the rust contribution guidelines [here](
88 //! https://rustc-dev-guide.rust-lang.org/getting-started.html).
89 //! The source for this documentation can be found on
90 //! [GitHub](https://github.com/rust-lang/rust).
91 //! To contribute changes, make sure you read the guidelines first, then submit
92 //! pull-requests for your suggested changes.
94 //! Contributions are appreciated! If you see a part of the docs that can be
95 //! improved, submit a PR, or chat with us first on [Discord][rust-discord]
98 //! # A Tour of The Rust Standard Library
100 //! The rest of this crate documentation is dedicated to pointing out notable
101 //! features of The Rust Standard Library.
103 //! ## Containers and collections
105 //! The [`option`] and [`result`] modules define optional and error-handling
106 //! types, [`Option<T>`] and [`Result<T, E>`]. The [`iter`] module defines
107 //! Rust's iterator trait, [`Iterator`], which works with the [`for`] loop to
108 //! access collections.
110 //! The standard library exposes three common ways to deal with contiguous
111 //! regions of memory:
113 //! * [`Vec<T>`] - A heap-allocated *vector* that is resizable at runtime.
114 //! * [`[T; n]`][array] - An inline *array* with a fixed size at compile time.
115 //! * [`[T]`][slice] - A dynamically sized *slice* into any other kind of contiguous
116 //! storage, whether heap-allocated or not.
118 //! Slices can only be handled through some kind of *pointer*, and as such come
119 //! in many flavors such as:
121 //! * `&[T]` - *shared slice*
122 //! * `&mut [T]` - *mutable slice*
123 //! * [`Box<[T]>`][owned slice] - *owned slice*
125 //! [`str`], a UTF-8 string slice, is a primitive type, and the standard library
126 //! defines many methods for it. Rust [`str`]s are typically accessed as
127 //! immutable references: `&str`. Use the owned [`String`] for building and
128 //! mutating strings.
130 //! For converting to strings use the [`format!`] macro, and for converting from
131 //! strings use the [`FromStr`] trait.
133 //! Data may be shared by placing it in a reference-counted box or the [`Rc`]
134 //! type, and if further contained in a [`Cell`] or [`RefCell`], may be mutated
135 //! as well as shared. Likewise, in a concurrent setting it is common to pair an
136 //! atomically-reference-counted box, [`Arc`], with a [`Mutex`] to get the same
139 //! The [`collections`] module defines maps, sets, linked lists and other
140 //! typical collection types, including the common [`HashMap<K, V>`].
142 //! ## Platform abstractions and I/O
144 //! Besides basic data types, the standard library is largely concerned with
145 //! abstracting over differences in common platforms, most notably Windows and
146 //! Unix derivatives.
148 //! Common types of I/O, including [files], [TCP], [UDP], are defined in the
149 //! [`io`], [`fs`], and [`net`] modules.
151 //! The [`thread`] module contains Rust's threading abstractions. [`sync`]
152 //! contains further primitive shared memory types, including [`atomic`] and
153 //! [`mpsc`], which contains the channel types for message passing.
156 //! [`MIN`]: i32::MIN
157 //! [`MAX`]: i32::MAX
158 //! [page for the module `std::i32`]: crate::i32
159 //! [TCP]: net::TcpStream
160 //! [The Rust Prelude]: prelude
161 //! [UDP]: net::UdpSocket
162 //! [`Arc`]: sync::Arc
163 //! [owned slice]: boxed
164 //! [`Cell`]: cell::Cell
165 //! [`FromStr`]: str::FromStr
166 //! [`HashMap<K, V>`]: collections::HashMap
167 //! [`Mutex`]: sync::Mutex
168 //! [`Option<T>`]: option::Option
170 //! [`RefCell`]: cell::RefCell
171 //! [`Result<T, E>`]: result::Result
172 //! [`Vec<T>`]: vec::Vec
173 //! [`atomic`]: sync::atomic
174 //! [`for`]: ../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
175 //! [`str`]: prim@str
176 //! [`mpsc`]: sync::mpsc
177 //! [`std::cmp`]: cmp
178 //! [`std::slice`]: slice
179 //! [`use std::env`]: env/index.html
180 //! [`use`]: ../book/ch07-02-defining-modules-to-control-scope-and-privacy.html
181 //! [crates.io]: https://crates.io
182 //! [deref-coercions]: ../book/ch15-02-deref.html#implicit-deref-coercions-with-functions-and-methods
183 //! [files]: fs::File
184 //! [multithreading]: thread
185 //! [other]: #what-is-in-the-standard-library-documentation
186 //! [primitive types]: ../book/ch03-02-data-types.html
187 //! [rust-discord]: https://discord.gg/rust-lang
189 #![cfg_attr(not(feature = "restricted-std"), stable(feature = "rust1", since = "1.0.0"))]
190 #![cfg_attr(feature = "restricted-std", unstable(feature = "restricted_std", issue = "none"))]
192 html_root_url = "https://doc.rust-lang.org/nightly/",
193 html_playground_url = "https://play.rust-lang.org/",
194 issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
195 test(no_crate_inject, attr(deny(warnings))),
196 test(attr(allow(dead_code, deprecated, unused_variables, unused_mut)))
198 // Don't link to std. We are std.
200 #![warn(deprecated_in_future)]
201 #![warn(missing_docs)]
202 #![warn(missing_debug_implementations)]
203 #![allow(explicit_outlives_requirements)]
204 #![allow(unused_lifetimes)]
205 // Tell the compiler to link to either panic_abort or panic_unwind
206 #![needs_panic_runtime]
207 // std may use features in a platform-specific way
208 #![allow(unused_features)]
209 #![cfg_attr(test, feature(print_internals, set_stdio, update_panic_count))]
211 all(target_vendor = "fortanix", target_env = "sgx"),
212 feature(slice_index_methods, coerce_unsized, sgx_platform)
214 #![cfg_attr(all(test, target_vendor = "fortanix", target_env = "sgx"), feature(fixed_size_array))]
215 // std is implemented with unstable features, many of which are internal
216 // compiler details that will never be stable
217 // NB: the following list is sorted to minimize merge conflicts.
218 #![feature(alloc_error_handler)]
219 #![feature(alloc_layout_extra)]
220 #![feature(allocator_api)]
221 #![feature(allocator_internals)]
222 #![feature(allow_internal_unsafe)]
223 #![feature(allow_internal_unstable)]
224 #![feature(arbitrary_self_types)]
225 #![feature(array_error_internals)]
227 #![feature(associated_type_bounds)]
228 #![feature(atomic_mut_ptr)]
229 #![feature(box_syntax)]
230 #![feature(c_variadic)]
231 #![feature(can_vector)]
232 #![feature(cfg_accessible)]
233 #![feature(cfg_target_has_atomic)]
234 #![feature(cfg_target_thread_local)]
235 #![feature(char_error_internals)]
236 #![feature(char_internals)]
238 #![feature(concat_idents)]
239 #![feature(const_cstr_unchecked)]
240 #![feature(const_fn_transmute)]
241 #![feature(const_ipv6)]
242 #![feature(const_raw_ptr_deref)]
243 #![feature(const_ipv4)]
244 #![feature(container_error_extra)]
245 #![feature(core_intrinsics)]
246 #![feature(custom_test_frameworks)]
247 #![feature(decl_macro)]
248 #![cfg_attr(bootstrap, feature(doc_alias))]
250 #![feature(doc_keyword)]
251 #![feature(doc_masked)]
252 #![feature(doc_spotlight)]
253 #![feature(dropck_eyepatch)]
254 #![feature(duration_constants)]
255 #![feature(exact_size_is_empty)]
256 #![feature(exhaustive_patterns)]
257 #![feature(extend_one)]
258 #![feature(external_doc)]
259 #![feature(fn_traits)]
260 #![feature(format_args_nl)]
261 #![feature(gen_future)]
262 #![feature(generator_trait)]
263 #![feature(global_asm)]
264 #![feature(hash_raw_entry)]
265 #![feature(hashmap_internals)]
266 #![feature(int_error_internals)]
267 #![feature(int_error_matching)]
268 #![feature(integer_atomics)]
269 #![feature(into_future)]
270 #![feature(lang_items)]
272 #![feature(link_args)]
274 #![feature(llvm_asm)]
275 #![feature(log_syntax)]
276 #![feature(maybe_uninit_extra)]
277 #![feature(maybe_uninit_ref)]
278 #![feature(maybe_uninit_slice)]
279 #![feature(min_specialization)]
280 #![feature(needs_panic_runtime)]
281 #![feature(negative_impls)]
282 #![feature(never_type)]
284 #![feature(nonnull_slice_from_raw_parts)]
285 #![feature(once_cell)]
286 #![feature(optin_builtin_traits)]
287 #![feature(or_patterns)]
288 #![feature(panic_info_message)]
289 #![feature(panic_internals)]
290 #![feature(panic_unwind)]
291 #![feature(prelude_import)]
292 #![feature(ptr_internals)]
294 #![feature(raw_ref_macros)]
295 #![feature(ready_macro)]
296 #![feature(renamed_spin_loop)]
297 #![feature(rustc_attrs)]
298 #![feature(rustc_private)]
299 #![feature(shrink_to)]
300 #![feature(slice_concat_ext)]
301 #![feature(slice_internals)]
302 #![feature(slice_ptr_get)]
303 #![feature(slice_ptr_len)]
304 #![feature(slice_strip)]
305 #![feature(staged_api)]
306 #![feature(std_internals)]
308 #![feature(stmt_expr_attributes)]
309 #![feature(str_internals)]
311 #![feature(thread_local)]
312 #![feature(toowned_clone_into)]
313 #![feature(total_cmp)]
314 #![feature(trace_macros)]
315 #![feature(try_reserve)]
316 #![feature(unboxed_closures)]
317 #![feature(unsafe_block_in_unsafe_fn)]
318 #![feature(untagged_unions)]
319 #![feature(unwind_attributes)]
320 #![feature(vec_into_raw_parts)]
321 #![feature(wake_trait)]
322 // NB: the above list is sorted to minimize merge conflicts.
323 #![default_lib_allocator]
325 // Explicitly import the prelude. The compiler uses this same unstable attribute
326 // to import the prelude implicitly when building crates that depend on std.
331 // Access to Bencher, etc.
335 #[allow(unused_imports)] // macros from `alloc` are not used on all platforms
337 extern crate alloc as alloc_crate;
339 #[allow(unused_extern_crates)]
342 // We always need an unwinder currently for backtraces
344 #[allow(unused_extern_crates)]
347 // During testing, this crate is not actually the "real" std library, but rather
348 // it links to the real std library, which was compiled from this same source
349 // code. So any lang items std defines are conditionally excluded (or else they
350 // would generate duplicate lang item errors), and any globals it defines are
351 // _not_ the globals used by "real" std. So this import, defined only during
352 // testing gives test-std access to real-std lang items and globals. See #2912
354 extern crate std as realstd;
356 // The standard macros that are not built-in to the compiler.
363 // Public module declarations and re-exports
364 #[stable(feature = "rust1", since = "1.0.0")]
365 pub use alloc_crate::borrow;
366 #[stable(feature = "rust1", since = "1.0.0")]
367 pub use alloc_crate::boxed;
368 #[stable(feature = "rust1", since = "1.0.0")]
369 pub use alloc_crate::fmt;
370 #[stable(feature = "rust1", since = "1.0.0")]
371 pub use alloc_crate::format;
372 #[stable(feature = "rust1", since = "1.0.0")]
373 pub use alloc_crate::rc;
374 #[stable(feature = "rust1", since = "1.0.0")]
375 pub use alloc_crate::slice;
376 #[stable(feature = "rust1", since = "1.0.0")]
377 pub use alloc_crate::str;
378 #[stable(feature = "rust1", since = "1.0.0")]
379 pub use alloc_crate::string;
380 #[stable(feature = "rust1", since = "1.0.0")]
381 pub use alloc_crate::vec;
382 #[stable(feature = "rust1", since = "1.0.0")]
384 #[stable(feature = "simd_arch", since = "1.27.0")]
387 #[stable(feature = "core_array", since = "1.36.0")]
389 #[stable(feature = "rust1", since = "1.0.0")]
391 #[stable(feature = "rust1", since = "1.0.0")]
393 #[stable(feature = "rust1", since = "1.0.0")]
395 #[stable(feature = "rust1", since = "1.0.0")]
397 #[stable(feature = "rust1", since = "1.0.0")]
398 pub use core::convert;
399 #[stable(feature = "rust1", since = "1.0.0")]
400 pub use core::default;
401 #[stable(feature = "rust1", since = "1.0.0")]
403 #[stable(feature = "core_hint", since = "1.27.0")]
405 #[stable(feature = "i128", since = "1.26.0")]
407 #[stable(feature = "rust1", since = "1.0.0")]
409 #[stable(feature = "rust1", since = "1.0.0")]
411 #[stable(feature = "rust1", since = "1.0.0")]
413 #[stable(feature = "rust1", since = "1.0.0")]
415 #[stable(feature = "rust1", since = "1.0.0")]
416 pub use core::intrinsics;
417 #[stable(feature = "rust1", since = "1.0.0")]
419 #[stable(feature = "rust1", since = "1.0.0")]
421 #[stable(feature = "rust1", since = "1.0.0")]
422 pub use core::marker;
423 #[stable(feature = "rust1", since = "1.0.0")]
425 #[stable(feature = "rust1", since = "1.0.0")]
427 #[stable(feature = "rust1", since = "1.0.0")]
428 pub use core::option;
429 #[stable(feature = "pin", since = "1.33.0")]
431 #[stable(feature = "rust1", since = "1.0.0")]
433 #[stable(feature = "rust1", since = "1.0.0")]
435 #[stable(feature = "rust1", since = "1.0.0")]
436 pub use core::result;
437 #[stable(feature = "i128", since = "1.26.0")]
439 #[stable(feature = "rust1", since = "1.0.0")]
441 #[stable(feature = "rust1", since = "1.0.0")]
443 #[stable(feature = "rust1", since = "1.0.0")]
445 #[stable(feature = "rust1", since = "1.0.0")]
447 #[stable(feature = "rust1", since = "1.0.0")]
472 #[unstable(feature = "once_cell", issue = "74465")]
475 #[stable(feature = "futures_api", since = "1.36.0")]
477 //! Types and Traits for working with asynchronous tasks.
480 #[stable(feature = "futures_api", since = "1.36.0")]
481 pub use core::task::*;
484 #[unstable(feature = "wake_trait", issue = "69912")]
485 pub use alloc::task::*;
488 #[stable(feature = "futures_api", since = "1.36.0")]
491 // Platform-abstraction modules
498 // Private support modules
502 // The runtime entry point and a few unstable public functions used by the
506 #[path = "../../backtrace/src/lib.rs"]
507 #[allow(dead_code, unused_attributes)]
510 // Pull in the `std_detect` crate directly into libstd. The contents of
511 // `std_detect` are in a different repository: rust-lang/stdarch.
513 // `std_detect` depends on libstd, but the contents of this module are
514 // set up in such a way that directly pulling it here works such that the
515 // crate uses the this crate as its libstd.
516 #[path = "../../stdarch/crates/std_detect/src/mod.rs"]
517 #[allow(missing_debug_implementations, missing_docs, dead_code)]
518 #[unstable(feature = "stdsimd", issue = "48556")]
523 #[unstable(feature = "stdsimd", issue = "48556")]
525 pub use std_detect::detect;
527 // Re-export macros defined in libcore.
528 #[stable(feature = "rust1", since = "1.0.0")]
529 #[allow(deprecated, deprecated_in_future)]
531 assert_eq, assert_ne, debug_assert, debug_assert_eq, debug_assert_ne, matches, r#try, todo,
532 unimplemented, unreachable, write, writeln,
535 // Re-export built-in macros defined through libcore.
536 #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
539 asm, assert, cfg, column, compile_error, concat, concat_idents, env, file, format_args,
540 format_args_nl, global_asm, include, include_bytes, include_str, line, llvm_asm, log_syntax,
541 module_path, option_env, stringify, trace_macros,
544 #[stable(feature = "core_primitive", since = "1.43.0")]
545 pub use core::primitive;
547 // Include a number of private modules that exist solely to provide
548 // the rustdoc documentation for primitive types. Using `include!`
549 // because rustdoc only looks for these modules at the crate level.
550 include!("primitive_docs.rs");
552 // Include a number of private modules that exist solely to provide
553 // the rustdoc documentation for the existing keywords. Using `include!`
554 // because rustdoc only looks for these modules at the crate level.
555 include!("keyword_docs.rs");
557 // This is required to avoid an unstable error when `restricted-std` is not
558 // enabled. The use of #![feature(restricted_std)] in rustc-std-workspace-std
559 // is unconditional, so the unstable feature needs to be defined somewhere.
560 #[cfg_attr(not(feature = "restricted-std"), unstable(feature = "restricted_std", issue = "none"))]
561 mod __restricted_std_workaround {}