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]. Contiguous here means that elements are laid out so that every element is the same distance from its neighbors.
• 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
• 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. Hints may be compile time or runtime.
• 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.
• f16Experimental
  Constants for the f16 half-precision floating point type.
• f128Experimental
  Constants for the f128 quadruple-precision floating point type.
• intrinsicsExperimental
  Compiler intrinsics.
• ioExperimental
  Traits, helpers, and type definitions for core I/O functionality.
• panickingExperimental
  Panic support for core
• patExperimental
  Helper module for exporting the pattern_type macro
• 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.
• unicodeExperimental

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_matchExperimental
  A macro for defining #[cfg] match-like statements.
• concat_bytesExperimental
  Concatenates literals into a byte slice.
• concat_identsExperimental
  Concatenates identifiers into one identifier.
• const_format_argsExperimental
  Same as format_args, but can be used in some const contexts.
• format_args_nlExperimental
  Same as format_args, but adds a newline in the end.
• 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.