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. ↩

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

A 32-bit floating-point type (specifically, the “binary32” type defined in IEEE 754-2008).

f64

A 64-bit floating-point type (specifically, the “binary64” type defined in IEEE 754-2008).

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, &T and &mut T.

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, also called “unit”.

usize

The pointer-sized unsigned integer type.

f16Experimental

A 16-bit floating-point type (specifically, the “binary16” type defined in IEEE 754-2008).

f128Experimental

A 128-bit floating-point type (specifically, the “binary128” type defined in IEEE 754-2008).

neverExperimental

The ! type, also called “never”.

Modules

alloc

Memory allocation APIs

array

Utilities for the array primitive type.

cell

Shareable mutable containers.

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.

fmt

Utilities for formatting and printing strings.

hint

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

iter

Composable external iteration.

marker

Primitive traits and types representing basic properties of types.

mem

Basic functions for dealing with memory.

num

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

ops

Overloadable operators.

option

Optional values.

panic

Panic support in the standard library.

prelude

The core prelude

ptr

Manually manage memory through raw pointers.

result

Error handling with the Result type.

sync

Synchronization primitives

autodiffExperimental

Unstable module containing the unstable autodiff macro.

fromExperimental

Unstable module containing the unstable From derive macro.

intrinsicsExperimental

Compiler intrinsics.

panickingExperimental

Panic support for core

ub_checksExperimental

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

Macros

assert

Asserts that a boolean expression is true at runtime.

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.

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.

assert_unsafe_preconditionExperimental

Checks that the preconditions of an unsafe function are followed.

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.

trace_macrosExperimental

Enables or disables tracing functionality used for debugging other macros.