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:

enum.cr
json/to_json.cr
yaml/to_yaml.cr

Constructors

Class Method Summary

Instance Method Summary

Macro Summary

Instance methods inherited from module Comparable(Enum)

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

Instance methods inherited from struct Value

==(other : JSON::Any)
==(other : YAML::Any)
==(other)
==
, dup dup

Instance methods inherited from class Object

! : Bool !, !=(other) !=, !~(other) !~, ==(other) ==, ===(other : JSON::Any)
===(other : YAML::Any)
===(other)
===
, =~(other) =~, as(type : Class) as, as?(type : Class) as?, class class, dup dup, hash
hash(hasher)
hash
, inspect(io : IO) : Nil
inspect : String
inspect
, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil! not_nil!, pretty_inspect(width = 79, newline = "\n", indent = 0) : String pretty_inspect, pretty_print(pp : PrettyPrint) : Nil pretty_print, responds_to?(name : Symbol) : Bool responds_to?, tap(&) 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 : String
to_s(io : IO) : Nil
to_s
, to_yaml(io : IO)
to_yaml
to_yaml
, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

Constructor 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 : String | IO) : self from_yaml

Constructor Detail

def self.from_value(value : Int) : 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

[View source]
def self.from_value?(value : Int) : 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

[View source]
def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node) #

[View source]
def self.new(pull : JSON::PullParser) #

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def self.parse(string : 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 "FortyTwo" or "FORTY_TWO" is found with any of these strings: "forty_two", "FortyTwo", "FORTY_TWO", "FORTYTWO", "fortytwo".

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

[View source]
def self.parse?(string : 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 "FortyTwo" or "FORTY_TWO" is found with any of these strings: "forty_two", "FortyTwo", "FORTY_TWO", "FORTYTWO", "fortytwo".

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

[View source]

Class Method Detail

def self.each(&) #

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

[View source]
def self.names : Array(String) #

Returns all enum members as an Array(String).

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

[View source]
def self.valid?(value : self) : Bool #

Returns true if the given value is an enum member, otherwise false. false if not member.

Color.valid?(Color::Red)   # => true
Color.valid?(Color.new(4)) # => false

NOTE This is a class method, not an instance method because an instance method .valid? is defined by the language when a user defines an enum member named Valid.


[View source]
def self.values : Array(self) #

Returns all enum members as an Array(self).

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

[View source]

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

[View source]
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)

[View source]
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)

[View source]
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

[View source]
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

[View source]
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.


[View source]
def clone #

[View source]
def each(&) #

Iterates each values in a Flags Enum.

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

[View source]
def hash(hasher) #

[View source]
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

[View source]
def to_f32 : Float32 #

Returns the value of this enum member as a Float32


[View source]
def to_f32! : Float32 #

Returns the value of this enum member as a Float32


[View source]
def to_f64 : Float64 #

Returns the value of this enum member as a Float64


[View source]
def to_f64! : Float64 #

Returns the value of this enum member as a Float64


[View source]
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

[View source]
def to_i16 : Int16 #

Returns the value of this enum member as a Int16


[View source]
def to_i16! : Int16 #

Returns the value of this enum member as a Int16


[View source]
def to_i32 : Int32 #

Returns the value of this enum member as a Int32


[View source]
def to_i32! : Int32 #

Returns the value of this enum member as a Int32


[View source]
def to_i64 : Int64 #

Returns the value of this enum member as a Int64


[View source]
def to_i64! : Int64 #

Returns the value of this enum member as a Int64


[View source]
def to_i8 : Int8 #

Returns the value of this enum member as a Int8


[View source]
def to_i8! : Int8 #

Returns the value of this enum member as a Int8


[View source]
def to_json(json : JSON::Builder) #

[View source]
def to_s(io : IO) : Nil #

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

See also: #to_s.


[View source]
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 vertical bars, 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"

[View source]
def to_u16 : UInt16 #

Returns the value of this enum member as a UInt16


[View source]
def to_u16! : UInt16 #

Returns the value of this enum member as a UInt16


[View source]
def to_u32 : UInt32 #

Returns the value of this enum member as a UInt32


[View source]
def to_u32! : UInt32 #

Returns the value of this enum member as a UInt32


[View source]
def to_u64 : UInt64 #

Returns the value of this enum member as a UInt64


[View source]
def to_u64! : UInt64 #

Returns the value of this enum member as a UInt64


[View source]
def to_u8 : UInt8 #

Returns the value of this enum member as a UInt8


[View source]
def to_u8! : UInt8 #

Returns the value of this enum member as a UInt8


[View source]
def to_yaml(yaml : YAML::Nodes::Builder) #

[View source]
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

[View source]
def ~ #

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


[View source]

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

[View source]