struct Union(*T)

Overview

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

When invoking a method on a union type, the language checks that the method exists and can be resolved (typed) for each type in the union. For this reason, adding instance methods to Union makes no sense and has no effect. However, adding class method to Union is possible and can be useful. One example is parsing JSON into one of many possible types.

Union is special in that it is a generic type but instantiating it might not return a union type:

Union(Int32 | String)      # => (Int32 | String)
Union(Int32)               # => Int32
Union(Int32, Int32, Int32) # => Int32

Defined in:

union.cr

Constructors

Class Method Summary

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.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node) #

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

[View source]
def self.new #

[View source]

Class Method Detail

def self.nilable? #

Returns true if this union includes the Nil type.

(Int32 | String).nilable? # => false
(Int32 | Nil).nilable?    # => true

[View source]