abstract struct Enum

Overview

Enum is the base type of all enums.

An enum is a set of integer values, where each value has an associated name. For example:

enum Color
  Red   # 0
  Green # 1
  Blue  # 2
end

Values start with the value 0 and are incremented by one, but can be overwritten.

To get the underlying value you invoke value on it:

Color::Green.value # => 1

Each constant (member) in the enum has the type of the enum:

typeof(Color::Red) # => Color

Flags enum

An enum can be marked with the @[Flags] attribute. This changes the default values:

@[Flags]
enum IOMode
  Read  # 1
  Write # 2
  Async # 4
end

Additionally, some methods change their behaviour.

Enums from integers

An enum can be created from an integer:

Color.new(1).to_s # => "Green"

Values that don't correspond to an enum's constants are allowed: the value will still be of type Color, but when printed you will get the underlying value:

Color.new(10).to_s # => "10"

This method is mainly intended to convert integers from C to enums in Crystal.

Question methods

An enum automatically defines question methods for each member, using String#underscore for the method name.

For example:

color = Color::Blue
color.red?  # => false
color.blue? # => true

mode = IOMode::Read | IOMode::Async
mode.read?  # => true
mode.write? # => false
mode.async? # => true

This is very convenient in case expressions:

case color
when .red?
  puts "Got red"
when .blue?
  puts "Got blue"
end

Included Modules

Defined in:

Class Method Summary

Instance Method Summary

Macro Summary

Instance methods inherited from module Comparable(self)

<(other : T) <, <=(other : T) <=, <=>(other : T) <=>, ==(other : T) ==, >(other : T) >, >=(other : T) >=

Instance methods inherited from struct Value

==(other) ==, dup dup

Instance methods inherited from class Object

!=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other)
===
, =~(other) =~, class class, dup dup, hash hash, inspect(io : IO)
inspect
inspect
, itself itself, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, tap(&block) tap, to_json(io : IO)
to_json
to_json
, to_pretty_json(indent : String = " ")
to_pretty_json(io : IO, indent : String = " ")
to_pretty_json
, to_s
to_s(io : IO)
to_s
, to_yaml(io : IO)
to_yaml
to_yaml
, try(&block) try

Class methods inherited from class Object

from_json(string_or_io, root : String) : self
from_json(string_or_io) : self
from_json
, from_yaml(string_or_io) : self from_yaml

Class Method Detail

def self.each(&block) #

Iterates each member of the enum. It won't iterate the None and All members of flags enums.

IOMode.each do |member, value|
  # yield IOMode::Read, 1
  # yield IOMode::Write, 2
  # yield IOMode::Async, 3
end

def self.from_value(value) : self #

Returns the enum member that has the given value, or raises if no such member exists.

Color.from_value(0) # => Color::Red
Color.from_value(1) # => Color::Green
Color.from_value(2) # => Color::Blue
Color.from_value(3) # raises Exception

def self.from_value?(value) : self? #

Returns the enum member that has the given value, or nil if no such member exists.

Color.from_value?(0) # => Color::Red
Color.from_value?(1) # => Color::Green
Color.from_value?(2) # => Color::Blue
Color.from_value?(3) # => nil

def self.names : Array(String) #

Returns all enum members as an Array(String).

Color.names # => ["Red", "Green", "Blue"]

def self.new(pull : JSON::PullParser) #

def self.new(pull : YAML::PullParser) #

def self.parse(string) : self #

Returns the enum member that has the given name, or raises ArgumentError if no such member exists. The comparison is made by using String#camelcase and String#downcase between string and the enum members names, so a member named "FourtyTwo" or "FOURTY_TWO" is found with any of these strings: "fourty_two", "FourtyTwo", "FOURTY_TWO", "FOURTYTWO", "fourtytwo".

Color.parse("Red")    # => Color::Red
Color.parse("BLUE")   # => Color::Blue
Color.parse("Yellow") # raises ArgumentError

def self.parse?(string) : self? #

Returns the enum member that has the given name, or nil if no such member exists. The comparison is made by using String#camelcase and String#downcase between string and the enum members names, so a member named "FourtyTwo" or "FOURTY_TWO" is found with any of these strings: "fourty_two", "FourtyTwo", "FOURTY_TWO", "FOURTYTWO", "fourtytwo".

Color.parse?("Red")    # => Color::Red
Color.parse?("BLUE")   # => Color::Blue
Color.parse?("Yellow") # => nil

def self.values : Array(self) #

Returns all enum members as an Array(self).

Color.values # => [Color::Red, Color::Green, Color::Blue]

Instance Method Detail

def &(other : self) #

Returns the enum member that results from applying a logical "and" operation between this enum member's value and other. This is mostly useful with flag enums.

(IOMode::Read | IOMode::Async) & IOMode::Read # => IOMode::Read

def +(other : Int) #

Returns the enum member that results from adding other to this enum member's value.

Color::Red + 1 # => Color::Green
Color::Red + 2 # => Color::Blue
Color::Red + 3 # => Color.new(3)

def -(other : Int) #

Returns the enum member that results from subtracting other to this enum member's value.

Color::Blue - 1 # => Color::Green
Color::Blue - 2 # => Color::Red
Color::Blue - 3 # => Color.new(-1)

def <=>(other : self) #

Compares this enum member against another, according to their underlying value.

Color::Red <=> Color::Blue  # => -1
Color::Blue <=> Color::Red  # => 1
Color::Blue <=> Color::Blue # => 0

def ==(other : self) #

Returns true if this enum member and other have the same underlying value.

Color::Red == Color::Red  # => true
Color::Red == Color::Blue # => false

def ^(other : self) #

Returns the enum member that results from applying a logical "xor" operation between this enum member's value and other. This is mostly useful with flag enums.


def clone #

def each(&block) #

Iterates each values in a Flags Enum.

(IOMode::Read | IOMode::Async).each do |member, value|
  # yield IOMode::Read, 1
  # yield IOMode::Async, 3
end

def hash #

Returns a hash value. This is the hash of the underlying value.


def includes?(other : self) #

Returns true if this enum member's value includes other. This performs a logical "and" between this enum member's value and other's, so instead of writing:

(member & value) != 0

you can write:

member.includes?(value)

The above is mostly useful with flag enums.

For example:

mode = IOMode::Read | IOMode::Write
mode.includes?(IOMode::Read)  # => true
mode.includes?(IOMode::Async) # => false

def to_f32 : Float32 #

Returns the value of this enum member as a Float32


def to_f64 : Float64 #

Returns the value of this enum member as a Float64


def to_i : Int32 #

Returns the value of this enum member as an Int32.

Color::Blue.to_i                    # => 2
(IOMode::Read | IOMode::Write).to_i # => 3

Color.new(10).to_i # => 10

def to_i16 : Int16 #

Returns the value of this enum member as a Int16


def to_i32 : Int32 #

Returns the value of this enum member as a Int32


def to_i64 : Int64 #

Returns the value of this enum member as a Int64


def to_i8 : Int8 #

Returns the value of this enum member as a Int8


def to_json(json : JSON::Builder) #

def to_s(io : IO) : Nil #

Appends a String representation of this enum member to the given io.

See also: #to_s.


def to_s : String #

Returns a String representation of this enum member. In the case of regular enums, this is just the name of the member. In the case of flag enums, it's the names joined by commas, or "None", if the value is zero.

If an enum's value doesn't match a member's value, the raw value is returned as a string.

Color::Red.to_s                     # => "Red"
IOMode::None.to_s                   # => "None"
(IOMode::Read | IOMode::Write).to_s # => "Read | Write"

Color.new(10).to_s # => "10"

def to_u16 : UInt16 #

Returns the value of this enum member as a UInt16


def to_u32 : UInt32 #

Returns the value of this enum member as a UInt32


def to_u64 : UInt64 #

Returns the value of this enum member as a UInt64


def to_u8 : UInt8 #

Returns the value of this enum member as a UInt8


def to_yaml(yaml : YAML::Builder) #

def |(other : self) #

Returns the enum member that results from applying a logical "or" operation between this enum member's value and other. This is mostly useful with flag enums.

(IOMode::Read | IOMode::Async) # => IOMode::Read | IOMode::Async

def ~ #

Returns the enum member that results from applying a logical "not" operation of this enum member's value.


Macro Detail

macro flags(*values) #

Convenience macro to create a combined enum (combines given members using #| (or) logical operator)

IOMode.flags(Read, Write) # => IOMode::Read | IOMode::Write