Crate core 

The Rust Core Library

The Rust Core Library is the dependency-free¹ foundation of The Rust Standard Library. It is the portable glue between the language and its libraries, defining the intrinsic and primitive building blocks of all Rust code. It links to no upstream libraries, no system libraries, and no libc.

The core library is minimal: it isn’t even aware of heap allocation, nor does it provide concurrency or I/O. These things require platform integration, and this library is platform-agnostic.

How to use the core library

Please note that all of these details are currently not considered stable.

This library is built on the assumption of a few existing symbols:

• memcpy, memmove, memset, memcmp, bcmp, strlen - These are core memory routines which are generated by Rust codegen backends. Additionally, this library can make explicit calls to strlen. Their signatures are the same as found in C, but there are extra assumptions about their semantics: For memcpy, memmove, memset, memcmp, and bcmp, if the n parameter is 0, the function is assumed to not be UB, even if the pointers are NULL or dangling. (Note that making extra assumptions about these functions is common among compilers: clang and GCC do the same.) These functions are often provided by the system libc, but can also be provided by the compiler-builtins crate. Note that the library does not guarantee that it will always make these assumptions, so Rust user code directly calling the C functions should follow the C specification! The advice for Rust user code is to call the functions provided by this library instead (such as ptr::copy).

• Panic handler - This function takes one argument, a &panic::PanicInfo. It is up to consumers of this core library to define this panic function; it is only required to never return. You should mark your implementation using #[panic_handler].

• rust_eh_personality - is used by the failure mechanisms of the compiler. This is often mapped to GCC’s personality function, but crates which do not trigger a panic can be assured that this function is never called. The lang attribute is called eh_personality.

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1. Strictly speaking, there are some symbols which are needed but they aren’t always necessary. ↩

Modules

alloc

Memory allocation APIs

any

Utilities for dynamic typing or type reflection.

arch

SIMD and vendor intrinsics module.

array

Utilities for the array primitive type.

ascii

Operations on ASCII strings and characters.

borrow

Utilities for working with borrowed data.

cell

Shareable mutable containers.

char

Utilities for the char primitive type.

clone

The Clone trait for types that cannot be ‘implicitly copied’.

cmp

Utilities for comparing and ordering values.

convert

Traits for conversions between types.

default

The Default trait for types with a default value.

error

Interfaces for working with Errors.

f32

Constants for the f32 single-precision floating point type.

f64

Constants for the f64 double-precision floating point type.

ffi

Platform-specific types, as defined by C.

fmt

Utilities for formatting and printing strings.

future

Asynchronous basic functionality.

hash

Generic hashing support.

hint

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

i8Deprecation planned

Redundant constants module for the i8 primitive type.

i16Deprecation planned

Redundant constants module for the i16 primitive type.

i32Deprecation planned

Redundant constants module for the i32 primitive type.

i64Deprecation planned

Redundant constants module for the i64 primitive type.

i128Deprecation planned

Redundant constants module for the i128 primitive type.

isizeDeprecation planned

Redundant constants module for the isize primitive 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 IP communication.

num

Numeric traits and functions for the built-in numeric types.

ops

Overloadable operators.

option

Optional values.

panic

Panic support in the standard library.

pin

Types that pin data to a location in memory.

prelude

The core prelude

primitive

This module reexports the primitive types to allow usage that is not possibly shadowed by other declared types.

ptr

Manually manage memory through raw pointers.

result

Error handling with the Result type.

slice

Slice management and manipulation.

str

String manipulation.

sync

Synchronization primitives

task

Types and Traits for working with asynchronous tasks.

time

Temporal quantification.

u8Deprecation planned

Redundant constants module for the u8 primitive type.

u16Deprecation planned

Redundant constants module for the u16 primitive type.

u32Deprecation planned

Redundant constants module for the u32 primitive type.

u64Deprecation planned

Redundant constants module for the u64 primitive type.

u128Deprecation planned

Redundant constants module for the u128 primitive type.

usizeDeprecation planned

Redundant constants module for the usize primitive type.

assert_matchesExperimental

Unstable module containing the unstable assert_matches macro.

async_iterExperimental

Composable asynchronous iteration.

autodiffExperimental

Unstable module containing the unstable autodiff macro.

bstrExperimental

The ByteStr type and trait implementations.

contractsExperimental

Unstable module containing the unstable contracts lang items and attribute macros.

f16Experimental

Constants for the f16 half-precision floating point type.

f128Experimental

Constants for the f128 quadruple-precision floating point type.

fromExperimental

Unstable module containing the unstable From derive macro.

intrinsicsExperimental

Compiler intrinsics.

ioExperimental

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

osExperimental

OS-specific functionality.

panickingExperimental

Panic support for core

patExperimental

Helper module for exporting the pattern_type macro

randomExperimental

Random value generation.

rangeExperimental

Experimental replacement range types

simdExperimental

Portable SIMD module.

ub_checksExperimental

Provides the assert_unsafe_precondition macro as well as some utility functions that cover common preconditions.

unsafe_binderExperimental

Operators used to turn types into unsafe binders and back.

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.

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.

file

Expands to the file name in which it was invoked.

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 UTF-8 encoded file as a string.

line

Expands to the line number on which it was invoked.

matches

Returns whether the given expression matches the provided pattern.

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.

stringify

Stringifies its arguments.

todo

Indicates unfinished code.

tryDeprecated

Unwraps a result or propagates its error.

unimplemented

Indicates unimplemented code by panicking with a message of “not implemented”.

unreachable

Indicates unreachable code.

write

Writes formatted data into a buffer.

writeln

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

assert_unsafe_preconditionExperimental

Checks that the preconditions of an unsafe function are followed.

cfg_selectExperimental

Selects code at compile-time based on cfg predicates.

concat_bytesExperimental

Concatenates literals into a byte slice.

const_format_argsExperimental

Same as format_args, but can be used in some const contexts.

log_syntaxExperimental

Prints passed tokens into the standard output.

pattern_typeExperimental

Creates a pattern type.

trace_macrosExperimental

Enables or disables tracing functionality used for debugging other macros.