lib.rs.html -- source
Description: Source to the Rust file `src/libstd/lib.rs`.
Keywords: rust, rustlang, rust-lang

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    //! # 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][crates.io]. It offers core types, like [`Vec<T>`] and
    //! [`Option<T>`], library-defined [operations on language
    //! primitives](#primitives), [standard macros](#macros), [I/O] and
    //! [multithreading], among [many other things][other].
    //!
    //! `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 <a href="#" onclick="focusSearchBar();">search
    //! bar</a> at the top of the page.
    //!
    //! Otherwise, you may want to jump to one of these useful sections:
    //!
    //! * [`std::*` modules](#modules)
    //! * [Primitive types](#primitives)
    //! * [Standard macros](#macros)
    //! * [The Rust Prelude](prelude/index.html)
    //!
    //! 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](#modules). 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](#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`](primitive.i32.html) 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`](i32/index.html) that documents the constant values [`MIN`] and
    //! [`MAX`](i32/constant.MAX.html) (rarely useful).
    //!
    //! Note the documentation for the primitives [`str`] and [`[T]`][slice] (also
    //! called 'slice'). Many method calls on [`String`] and [`Vec<T>`] are actually
    //! calls to methods on [`str`] and [`[T]`][slice] respectively, via [deref
    //! coercions][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](#macros) (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](
    //! https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md).
    //! The source for this documentation can be found on [Github](https://github.com/rust-lang).
    //! 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][rust-discord]
    //! #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:
    //!
    //! * [`Vec<T>`] - A heap-allocated *vector* that is resizable at runtime.
    //! * [`[T; n]`][array] - An inline *array* with a fixed size at compile time.
    //! * [`[T]`][slice] - 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] - *owned slice*
    //!
    //! [`str`], a UTF-8 string slice, is a primitive type, and the standard library
    //! defines many methods for it. Rust [`str`]s 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.
    //!
    //! [I/O]: io/index.html
    //! [`MIN`]: i32/constant.MIN.html
    //! [TCP]: net/struct.TcpStream.html
    //! [The Rust Prelude]: prelude/index.html
    //! [UDP]: net/struct.UdpSocket.html
    //! [`Arc`]: sync/struct.Arc.html
    //! [owned slice]: boxed/index.html
    //! [`Cell`]: cell/struct.Cell.html
    //! [`FromStr`]: str/trait.FromStr.html
    //! [`HashMap<K, V>`]: collections/struct.HashMap.html
    //! [`Iterator`]: iter/trait.Iterator.html
    //! [`Mutex`]: sync/struct.Mutex.html
    //! [`Option<T>`]: option/enum.Option.html
    //! [`Rc`]: rc/struct.Rc.html
    //! [`RefCell`]: cell/struct.RefCell.html
    //! [`Result<T, E>`]: result/enum.Result.html
    //! [`String`]: string/struct.String.html
    //! [`Vec<T>`]: vec/struct.Vec.html
    //! [array]: primitive.array.html
    //! [slice]: primitive.slice.html
    //! [`atomic`]: sync/atomic/index.html
    //! [`collections`]: collections/index.html
    //! [`for`]: ../book/ch03-05-control-flow.html#looping-through-a-collection-with-for
    //! [`format!`]: macro.format.html
    //! [`fs`]: fs/index.html
    //! [`io`]: io/index.html
    //! [`iter`]: iter/index.html
    //! [`mpsc`]: sync/mpsc/index.html
    //! [`net`]: net/index.html
    //! [`option`]: option/index.html
    //! [`result`]: result/index.html
    //! [`std::cmp`]: cmp/index.html
    //! [`std::slice`]: slice/index.html
    //! [`str`]: primitive.str.html
    //! [`sync`]: sync/index.html
    //! [`thread`]: thread/index.html
    //! [`use std::env`]: env/index.html
    //! [`use`]: ../book/ch07-02-defining-modules-to-control-scope-and-privacy.html
    //! [crates.io]: https://crates.io
    //! [deref-coercions]: ../book/ch15-02-deref.html#implicit-deref-coercions-with-functions-and-methods
    //! [files]: fs/struct.File.html
    //! [multithreading]: thread/index.html
    //! [other]: #what-is-in-the-standard-library-documentation
    //! [primitive types]: ../book/ch03-02-data-types.html
    //! [rust-discord]: https://discord.gg/rust-lang

    #![stable(feature = "rust1", since = "1.0.0")]
    #![doc(
        html_root_url = "https://doc.rust-lang.org/nightly/",
        html_playground_url = "https://play.rust-lang.org/",
        issue_tracker_base_url = "https://github.com/rust-lang/rust/issues/",
        test(no_crate_inject, attr(deny(warnings))),
        test(attr(allow(dead_code, deprecated, unused_variables, unused_mut)))
    )]
    // Don't link to std. We are std.
    #![no_std]
    #![warn(deprecated_in_future)]
    #![warn(missing_docs)]
    #![warn(missing_debug_implementations)]
    #![deny(intra_doc_link_resolution_failure)] // rustdoc is run without -D warnings
    #![allow(explicit_outlives_requirements)]
    #![allow(unused_lifetimes)]
    // Tell the compiler to link to either panic_abort or panic_unwind
    #![needs_panic_runtime]
    // std may use features in a platform-specific way
    #![allow(unused_features)]
    #![cfg_attr(test, feature(print_internals, set_stdio, update_panic_count))]
    #![cfg_attr(
        all(target_vendor = "fortanix", target_env = "sgx"),
        feature(slice_index_methods, coerce_unsized, sgx_platform, ptr_wrapping_offset_from)
    )]
    #![cfg_attr(
        all(test, target_vendor = "fortanix", target_env = "sgx"),
        feature(fixed_size_array, maybe_uninit_extra)
    )]
    // std is implemented with unstable features, many of which are internal
    // compiler details that will never be stable
    // NB: the following list is sorted to minimize merge conflicts.
    #![feature(alloc_error_handler)]
    #![feature(alloc_layout_extra)]
    #![feature(allocator_api)]
    #![feature(allocator_internals)]
    #![feature(allow_internal_unsafe)]
    #![feature(allow_internal_unstable)]
    #![feature(arbitrary_self_types)]
    #![feature(array_error_internals)]
    #![feature(asm)]
    #![feature(associated_type_bounds)]
    #![feature(atomic_mut_ptr)]
    #![feature(box_syntax)]
    #![feature(c_variadic)]
    #![feature(cfg_accessible)]
    #![feature(can_vector)]
    #![feature(cfg_target_has_atomic)]
    #![feature(cfg_target_thread_local)]
    #![feature(char_error_internals)]
    #![feature(char_internals)]
    #![feature(clamp)]
    #![feature(concat_idents)]
    #![feature(const_cstr_unchecked)]
    #![feature(const_raw_ptr_deref)]
    #![feature(container_error_extra)]
    #![feature(core_intrinsics)]
    #![feature(custom_test_frameworks)]
    #![feature(decl_macro)]
    #![feature(doc_alias)]
    #![feature(doc_cfg)]
    #![feature(doc_keyword)]
    #![feature(doc_masked)]
    #![feature(dropck_eyepatch)]
    #![feature(duration_constants)]
    #![feature(exact_size_is_empty)]
    #![feature(exhaustive_patterns)]
    #![feature(extend_one)]
    #![feature(external_doc)]
    #![feature(fn_traits)]
    #![feature(format_args_nl)]
    #![feature(future_readiness_fns)]
    #![feature(gen_future)]
    #![feature(generator_trait)]
    #![feature(global_asm)]
    #![feature(hash_raw_entry)]
    #![feature(hashmap_internals)]
    #![feature(int_error_internals)]
    #![feature(int_error_matching)]
    #![feature(into_future)]
    #![feature(integer_atomics)]
    #![feature(lang_items)]
    #![feature(libc)]
    #![feature(link_args)]
    #![feature(linkage)]
    #![feature(llvm_asm)]
    #![feature(log_syntax)]
    #![feature(maybe_uninit_ref)]
    #![feature(maybe_uninit_slice)]
    #![feature(needs_panic_runtime)]
    #![feature(negative_impls)]
    #![feature(never_type)]
    #![feature(nll)]
    #![feature(optin_builtin_traits)]
    #![feature(or_patterns)]
    #![feature(panic_info_message)]
    #![feature(panic_internals)]
    #![feature(panic_unwind)]
    #![feature(prelude_import)]
    #![feature(ptr_internals)]
    #![feature(raw)]
    #![feature(raw_ref_macros)]
    #![feature(renamed_spin_loop)]
    #![feature(rustc_attrs)]
    #![feature(rustc_private)]
    #![feature(shrink_to)]
    #![feature(slice_concat_ext)]
    #![feature(slice_internals)]
    #![feature(min_specialization)]
    #![feature(staged_api)]
    #![feature(std_internals)]
    #![feature(stdsimd)]
    #![feature(stmt_expr_attributes)]
    #![feature(str_internals)]
    #![feature(test)]
    #![feature(thread_local)]
    #![feature(toowned_clone_into)]
    #![feature(total_cmp)]
    #![feature(trace_macros)]
    #![cfg_attr(bootstrap, feature(track_caller))]
    #![feature(try_reserve)]
    #![feature(unboxed_closures)]
    #![feature(unsafe_block_in_unsafe_fn)]
    #![feature(untagged_unions)]
    #![feature(unwind_attributes)]
    #![feature(vec_into_raw_parts)]
    #![feature(wake_trait)]
    // NB: the above list is sorted to minimize merge conflicts.
    #![default_lib_allocator]

    // Explicitly import the prelude. The compiler uses this same unstable attribute
    // to import the prelude implicitly when building crates that depend on std.
    #[prelude_import]
    #[allow(unused)]
    use prelude::v1::*;

    // Access to Bencher, etc.
    #[cfg(test)]
    extern crate test;

    #[allow(unused_imports)] // macros from `alloc` are not used on all platforms
    #[macro_use]
    extern crate alloc as alloc_crate;
    #[doc(masked)]
    #[allow(unused_extern_crates)]
    extern crate libc;

    // We always need an unwinder currently for backtraces
    #[doc(masked)]
    #[allow(unused_extern_crates)]
    extern crate unwind;

    // During testing, this crate is not actually the "real" std library, but rather
    // it links to the real std library, which was compiled from this same source
    // code. So any lang items std defines are conditionally excluded (or else they
    // would generate duplicate lang item errors), and any globals it defines are
    // _not_ the globals used by "real" std. So this import, defined only during
    // testing gives test-std access to real-std lang items and globals. See #2912
    #[cfg(test)]
    extern crate std as realstd;

    // The standard macros that are not built-in to the compiler.
    #[macro_use]
    mod macros;

    // The Rust prelude
    pub mod prelude;

    // Public module declarations and re-exports
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::borrow;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::boxed;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::fmt;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::format;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::rc;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::slice;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::str;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::string;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use alloc_crate::vec;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::any;
    #[stable(feature = "simd_arch", since = "1.27.0")]
    #[doc(no_inline)]
    pub use core::arch;
    #[stable(feature = "core_array", since = "1.36.0")]
    pub use core::array;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::cell;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::char;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::clone;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::cmp;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::convert;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::default;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::hash;
    #[stable(feature = "core_hint", since = "1.27.0")]
    pub use core::hint;
    #[stable(feature = "i128", since = "1.26.0")]
    pub use core::i128;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::i16;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::i32;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::i64;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::i8;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::intrinsics;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::isize;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::iter;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::marker;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::mem;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::ops;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::option;
    #[stable(feature = "pin", since = "1.33.0")]
    pub use core::pin;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::ptr;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::raw;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::result;
    #[stable(feature = "i128", since = "1.26.0")]
    pub use core::u128;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::u16;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::u32;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::u64;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::u8;
    #[stable(feature = "rust1", since = "1.0.0")]
    pub use core::usize;

    pub mod f32;
    pub mod f64;

    #[macro_use]
    pub mod thread;
    pub mod ascii;
    pub mod backtrace;
    pub mod collections;
    pub mod env;
    pub mod error;
    pub mod ffi;
    pub mod fs;
    pub mod io;
    pub mod net;
    pub mod num;
    pub mod os;
    pub mod panic;
    pub mod path;
    pub mod process;
    pub mod sync;
    pub mod time;

    #[stable(feature = "futures_api", since = "1.36.0")]
    pub mod task {
        //! Types and Traits for working with asynchronous tasks.

        #[doc(inline)]
        #[stable(feature = "futures_api", since = "1.36.0")]
        pub use core::task::*;

        #[doc(inline)]
        #[unstable(feature = "wake_trait", issue = "69912")]
        pub use alloc::task::*;
    }

    #[stable(feature = "futures_api", since = "1.36.0")]
    pub mod future;

    // Platform-abstraction modules
    #[macro_use]
    mod sys_common;
    mod sys;

    pub mod alloc;

    // Private support modules
    mod memchr;
    mod panicking;

    // The runtime entry point and a few unstable public functions used by the
    // compiler
    pub mod rt;

    // Pull in the `std_detect` crate directly into libstd. The contents of
    // `std_detect` are in a different repository: rust-lang/stdarch.
    //
    // `std_detect` depends on libstd, but the contents of this module are
    // set up in such a way that directly pulling it here works such that the
    // crate uses the this crate as its libstd.
    #[path = "../stdarch/crates/std_detect/src/mod.rs"]
    #[allow(missing_debug_implementations, missing_docs, dead_code)]
    #[unstable(feature = "stdsimd", issue = "48556")]
    #[cfg(not(test))]
    mod std_detect;

    #[doc(hidden)]
    #[unstable(feature = "stdsimd", issue = "48556")]
    #[cfg(not(test))]
    pub use std_detect::detect;

    // Re-export macros defined in libcore.
    #[stable(feature = "rust1", since = "1.0.0")]
    #[allow(deprecated, deprecated_in_future)]
    pub use core::{
        assert_eq, assert_ne, debug_assert, debug_assert_eq, debug_assert_ne, matches, r#try, todo,
        unimplemented, unreachable, write, writeln,
    };

    // Re-export built-in macros defined through libcore.
    #[stable(feature = "builtin_macro_prelude", since = "1.38.0")]
    #[allow(deprecated)]
    pub use core::{
        asm, assert, cfg, column, compile_error, concat, concat_idents, env, file, format_args,
        format_args_nl, global_asm, include, include_bytes, include_str, line, llvm_asm, log_syntax,
        module_path, option_env, stringify, trace_macros,
    };

    #[stable(feature = "core_primitive", since = "1.43.0")]
    pub use core::primitive;

    // Include a number of private modules that exist solely to provide
    // the rustdoc documentation for primitive types. Using `include!`
    // because rustdoc only looks for these modules at the crate level.
    include!("primitive_docs.rs");

    // Include a number of private modules that exist solely to provide
    // the rustdoc documentation for the existing keywords. Using `include!`
    // because rustdoc only looks for these modules at the crate level.
    include!("keyword_docs.rs");