API

• ArgumentError

  Raised when the arguments are wrong and there isn't a more specific Exception class.

• Array(T)

  An Array is an ordered, integer-indexed collection of objects of type T.

• Atomic(T)

  A value that may be updated atomically.

• Base64

  The Base64 module provides for the encoding (#encode, #strict_encode, #urlsafe_encode) and decoding (#decode) of binary data using a base64 representation.

• Benchmark

  The Benchmark module provides methods for benchmarking Crystal code, giving detailed reports on the time and memory taken for each task.

• BigDecimal

  A BigDecimal can represent arbitrarily large precision decimals.

• BigFloat

  A BigFloat can represent arbitrarily large floats.

• BigInt

  A BigInt can represent arbitrarily large integers.

• BigRational

  Rational numbers are represented as the quotient of arbitrarily large numerators and denominators.

• BitArray

  BitArray is an array data structure that compactly stores bits.

• Bool

  Bool has only two possible values: true and false.

• Box(T)

  A Box allows turning any object to a Void* and back.

• Bytes

  A convenient alias for the most common slice type, a slice of bytes, used for example in IO#read and IO#write.

• CSV

  Provides methods and classes for parsing and generating CSV (comma-separated values) strings.

• Channel(T)

  A Channel enables concurrent communication between fibers.

• Char

  A Char represents a Unicode code point.

• Class
• Colorize

  With Colorize you can change the fore- and background colors and text decorations when rendering text on terminals supporting ANSI escape codes.

• Comparable(T)

  The Comparable mixin is used by classes whose objects may be ordered.

• Complex

  A complex number is a number represented in the form a + bi.

• Compress
• Crypto
• Crystal
• Deprecated

  This annotation marks features as deprecated.

• Deque(T)

  A Deque ("double-ended queue") is a collection of objects of type T that behaves much like an Array.

• Digest

  Digest is the base type of hashing algorithms like Digest::MD5, Digest::SHA1, Digest::SHA256, or Digest::SHA512.

• Dir

  Objects of class Dir are directory streams representing directories in the underlying file system.

• DivisionByZeroError

  Raised when attempting to divide an integer by 0.

• ECR

  Embedded Crystal (ECR) is a template language for embedding Crystal code into other text, that includes but is not limited to HTML.

• ENV

  ENV is a hash-like accessor for environment variables.

• Enum

  Enum is the base type of all enums.

• Enumerable(T)

  The Enumerable mixin provides collection classes with several traversal, searching, filtering and querying methods.

• Errno

  Errno wraps and gives access to libc's errno.

• Exception

  Represents errors that occur during application execution.

• Experimental

  This annotation marks methods, classes, constants, and macros as experimental.

• Fiber

  A Fiber is a light-weight execution unit managed by the Crystal runtime.

• File

  A File instance represents a file entry in the local file system and allows using it as an IO.

• FileUtils

  NOTE To use FileUtils, you must explicitly import it with require "file_utils"

• Flags

  An enum can be marked with @[Flags].

• Float

  Float is the base type of all floating point numbers.

• Float32
• Float64
• GC
• HTML

  Provides HTML escaping and unescaping methods.

• HTTP

  The HTTP module contains HTTP::Client, HTTP::Server and HTTP::WebSocket implementations.

• Hash(K, V)

  A Hash represents a collection of key-value mappings, similar to a dictionary.

• INI

  NOTE To use INI, you must explicitly import it with require "ini"

• IO

  The IO class is the basis for all input and output in Crystal.

• IPSocket

  NOTE To use IPSocket, you must explicitly import it with require "socket/ip_socket"

• IndexError

  Raised when the given index is invalid.

• Indexable(T)

  A container that allows accessing elements via a numeric index.

• Int

  Int is the base type of all integer types.

• Int128
• Int16
• Int32
• Int64
• Int8
• Intrinsics
• InvalidBigDecimalException
• InvalidByteSequenceError
• Iterable(T)

  The Iterable mixin provides convenience methods to collection classes that provide an #each method that returns an Iterator over the collection.

• Iterator(T)

  An Iterator allows processing sequences lazily, as opposed to Enumerable which processes sequences eagerly and produces an Array in most of its methods.

• JSON

  The JSON module allows parsing and generating JSON documents.

• KeyError

  Raised when the specified key is not found.

• LLVM
• Levenshtein

  Levenshtein distance methods.

• Link

  A lib can be marked with @[Link(lib : String, *, ldflags : String, static : Bool, framework : String, pkg_config : String, wasm_import_module : String, dll : String)] to declare the library that should be linked when compiling the program.

• Log

  The Log class provides a logging utility that you can use to output messages.

• MIME

  This module implements a global MIME registry.

• Math
• Mutex

  A fiber-safe mutex.

• NamedTuple(**T)

  A named tuple is a fixed-size, immutable, stack-allocated mapping of a fixed set of keys to values.

• Nil

  The Nil type has only one possible value: nil.

• NilAssertionError

  Raised when a not_nil! assertion fails.

• NoReturn

  Some expressions won't return to the current scope and therefore have no return type.

• NotImplementedError

  Raised when a method is not implemented.

• Number

  The top-level number type.

• OAuth

  The OAuth module provides an OAuth::Consumer as specified by RFC 5849.

• OAuth2

  The OAuth module provides an OAuth2::Client as specified by RFC 6749.

• Object

  Object is the base type of all Crystal objects.

• OpenSSL

  The OpenSSL module allows for access to Secure Sockets Layer (SSL) and Transport Layer Security (TLS) encryption, as well as classes for encrypting data, decrypting data, and computing hashes.

• OptionParser

  OptionParser is a class for command-line options processing.

• OverflowError

  Raised when the result of an arithmetic operation is outside of the range that can be represented within the given operands types.

• Path

  A Path represents a filesystem path and allows path-handling operations such as querying its components as well as semantic manipulations.

• Pointer(T)

  A typed pointer to some memory.

• PrettyPrint

  This class implements a pretty printing algorithm.

• Proc(*T, R)

  A Proc represents a function pointer with an optional context (the closure data).

• Process
• Random

  Random provides an interface for random values generation, using a pseudo random number generator (PRNG).

• Range(B, E)

  A Range represents an interval: a set of values with a beginning and an end.

• Reference

  Reference is the base class of classes you define in your program.

• ReferenceStorage(T)

  ReferenceStorage(T) provides the minimum storage for the instance data of an object of type T.

  EXPERIMENTAL This type's API is still under development. Join the discussion about custom reference allocation at #13481.

• Regex

  A Regex represents a regular expression, a pattern that describes the contents of strings.

• RuntimeError

  Raised when there is an internal runtime error

• SemanticVersion

  Conforms to Semantic Versioning 2.0.0

• Set(T)

  Set implements a collection of values with no duplicates.

• Signal

  Safely handle inter-process signals on POSIX systems.

• Slice(T)

  A Slice is a Pointer with an associated size.

• Socket
• Spec

  Crystal's built-in testing library.

• StaticArray(T, N)

  A fixed-size, stack allocated array.

• Steppable

  Implements a #step method for iterating from a value.

• String

  A String represents an immutable sequence of UTF-8 characters.

• StringPool

  A string pool is a collection of strings.

• StringScanner

  StringScanner provides for lexical scanning operations on a String.

• Struct

  Struct is the base type of structs you create in your program.

• Symbol

  A symbol is a constant that is identified by a name without you having to give it a numeric value.

• Sync

  Synchronization primitives to build concurrent-safe and parallel-safe data structures, so we can embrace concurrency and parallelism with more serenity.

• Syscall

  EXPERIMENTAL

• System
• SystemError

  This module can be included in any Exception subclass that is used to wrap some system error (Errno or WinError).

• TCPServer

  A Transmission Control Protocol (TCP/IP) server.

• TCPSocket

  A Transmission Control Protocol (TCP/IP) socket.

• TargetFeature

  The annotation allows to assume special CPU model/features for a method.

• Termios

  DEPRECATED

• Time

  Time represents a date-time instant in incremental time observed in a specific time zone.

• Tuple(*T)

  A tuple is a fixed-size, immutable, stack-allocated sequence of values of possibly different types.

• TypeCastError

  Raised when the type cast failed.

• UDPSocket

  A User Datagram Protocol (UDP) socket.

• UInt128
• UInt16
• UInt32
• UInt64
• UInt8
• UNIXServer

  A local interprocess communication server socket.

• UNIXSocket

  A local interprocess communication clientsocket.

• URI

  This class represents a URI reference as defined by RFC 3986: Uniform Resource Identifier (URI): Generic Syntax.

• UUID

  Represents a UUID (Universally Unique IDentifier).

• Unicode

  Provides the Unicode::CaseOptions enum for special case conversions like Turkic.

• Union(*T)

  A union type represents the possibility of a variable or an expression having more than one possible type at compile time.

• VaList
• Value

  Value is the base type of the primitive types (Nil, Bool, Char, Number), Symbol, Pointer, Tuple, StaticArray and all structs.

• Void

  Similar in usage to Nil.

• WaitGroup

  Suspend execution until a collection of fibers are finished.

• WasiError
• WeakRef(T)

  Weak Reference class that allows a referenced object to be garbage-collected.

• WinError

  WinError represents Windows' System Error Codes.

• XML

  The XML module allows parsing and generating XML documents.

• YAML

  The YAML module provides serialization and deserialization of YAML version 1.1 to/from native Crystal data structures, with the additional independent types specified in http://yaml.org/type/