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.
Please note that all of these details are currently not considered stable.
This library is built on the assumption of a few existing symbols:
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
bcmp, if the
nparameter is 0, the function is assumed to not be UB. Furthermore, for
memcpy, if source and target pointer are equal, the function is assumed to not be UB. (Note that these are standard assumptions 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
rust_begin_panic- This function takes four arguments, a
&'static str, and two
u32’s. These four arguments dictate the panic message, the file at which panic was invoked, and the line and column inside the file. It is up to consumers of this core library to define this panic function; it is only required to never return. This requires a
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
langattribute is called
Strictly speaking, there are some symbols which are needed but they aren’t always necessary. ↩
!type, also called “never”.
- A fixed-size array, denoted
[T; N], for the element type,
T, and the non-negative compile-time constant size,
- The boolean type.
- A character type.
- A 32-bit floating point type (specifically, the “binary32” type defined in IEEE 754-2008).
- A 64-bit floating point type (specifically, the “binary64” type defined in IEEE 754-2008).
- Function pointers, like
fn(usize) -> bool.
- The 8-bit signed integer type.
- The 16-bit signed integer type.
- The 32-bit signed integer type.
- The 64-bit signed integer type.
- The 128-bit signed integer type.
- The pointer-sized signed integer type.
- Raw, unsafe pointers,
*const T, and
- A dynamically-sized view into a contiguous sequence,
[T]. Contiguous here means that elements are laid out so that every element is the same distance from its neighbors.
- String slices.
- A finite heterogeneous sequence,
(T, U, ..).
- The 8-bit unsigned integer type.
- The 16-bit unsigned integer type.
- The 32-bit unsigned integer type.
- The 64-bit unsigned integer type.
- The 128-bit unsigned integer type.
()type, also called “unit”.
- The pointer-sized unsigned integer type.
- assert_matchesExperimentalUnstable module containing the unstable
- async_iterExperimentalComposable asynchronous iteration.
- errorExperimentalInterfaces for working with Errors.
- intrinsicsExperimentalCompiler intrinsics.
- ioExperimentalTraits, helpers, and type definitions for core I/O functionality.
- netExperimentalNetworking primitives for IP communication.
- panickingExperimentalPanic support for core
- simdExperimentalPortable SIMD module.
- Memory allocation APIs
- Utilities for dynamic typing or type reflection.
- SIMD and vendor intrinsics module.
- Utilities for the array primitive type.
- Operations on ASCII strings and characters.
- Utilities for working with borrowed data.
- Shareable mutable containers.
- Utilities for the
Clonetrait for types that cannot be ‘implicitly copied’.
- Utilities for comparing and ordering values.
- Traits for conversions between types.
Defaulttrait for types with a default value.
- Constants for the
f32single-precision floating point type.
- Constants for the
f64double-precision floating point type.
- Platform-specific types, as defined by C.
- Utilities for formatting and printing strings.
- Asynchronous basic functionality.
- Generic hashing support.
- Hints to compiler that affects how code should be emitted or optimized. Hints may be compile time or runtime.
- i8Deprecation plannedRedundant constants module for the
- i16Deprecation plannedRedundant constants module for the
- i32Deprecation plannedRedundant constants module for the
- i64Deprecation plannedRedundant constants module for the
- i128Deprecation plannedRedundant constants module for the
- isizeDeprecation plannedRedundant constants module for the
- Composable external iteration.
- Primitive traits and types representing basic properties of types.
- Basic functions for dealing with memory.
- Numeric traits and functions for the built-in numeric types.
- Overloadable operators.
- Optional values.
- Panic support in the standard library.
- Types that pin data to its location in memory.
- The core prelude
- This module reexports the primitive types to allow usage that is not possibly shadowed by other declared types.
- Manually manage memory through raw pointers.
- Error handling with the
- Slice management and manipulation.
- String manipulation.
- Synchronization primitives
- Types and Traits for working with asynchronous tasks.
- Temporal quantification.
- u8Deprecation plannedRedundant constants module for the
- u16Deprecation plannedRedundant constants module for the
- u32Deprecation plannedRedundant constants module for the
- u64Deprecation plannedRedundant constants module for the
- u128Deprecation plannedRedundant constants module for the
- usizeDeprecation plannedRedundant constants module for the
- cfg_matchExperimentalA macro for defining
- concat_bytesExperimentalConcatenates literals into a byte slice.
- concat_identsExperimentalConcatenates identifiers into one identifier.
- const_format_argsExperimentalSame as
format_args, but can be used in some const contexts.
- format_args_nlExperimentalSame as
format_args, but adds a newline in the end.
- log_syntaxExperimentalPrints passed tokens into the standard output.
- trace_macrosExperimentalEnables or disables tracing functionality used for debugging other macros.
- Asserts that a boolean expression is
- Asserts that two expressions are equal to each other (using
- Asserts that two expressions are not equal to each other (using
- Evaluates boolean combinations of configuration flags at compile-time.
- Expands to the column number at which it was invoked.
- Causes compilation to fail with the given error message when encountered.
- Concatenates literals into a static string slice.
- Asserts that a boolean expression is
- Asserts that two expressions are equal to each other.
- Asserts that two expressions are not equal to each other.
- Inspects an environment variable at compile time.
- Expands to the file name in which it was invoked.
- Constructs parameters for the other string-formatting macros.
- Parses a file as an expression or an item according to the context.
- Includes a file as a reference to a byte array.
- Includes a UTF-8 encoded file as a string.
- Expands to the line number on which it was invoked.
- Returns whether the given expression matches any of the given patterns.
- Expands to a string that represents the current module path.
- Optionally inspects an environment variable at compile time.
- Panics the current thread.
- Stringifies its arguments.
- Indicates unfinished code.
- tryDeprecatedUnwraps a result or propagates its error.
- Indicates unimplemented code by panicking with a message of “not implemented”.
- Indicates unreachable code.
- Writes formatted data into a buffer.
- Write formatted data into a buffer, with a newline appended.