# struct Union(*T)

- Union(*T)
- Value
- Object

##
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

- .new(ctx : YAML::ParseContext, node : YAML::Nodes::Node)
- .new(pull : JSON::PullParser)
- .new

##
Class Method Summary

- .from_json_object_key?(key : String)

##
Instance Method Summary

- #initialize

### Instance methods inherited from struct `Value`

==(other : Log::Metadata::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(hasher)
hash hash, in?(collection : Object) : Bool
in?(*values : Object) : Bool in?, inspect(io : IO) : Nil
inspect : String inspect, is_a?(type : Class) : Bool is_a?, itself itself, nil? : Bool nil?, not_nil!(message)
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) : Nil
to_json : String to_json, to_pretty_json(indent : String = " ") : String
to_pretty_json(io : IO, indent : String = " ") : Nil to_pretty_json, to_s(io : IO) : Nil
to_s : String to_s, to_yaml(io : IO) : Nil
to_yaml : String to_yaml, try(&) try, unsafe_as(type : T.class) forall T unsafe_as

### Class methods inherited from class `Object`

from_json(string_or_io : String | IO, root : String)
from_json(string_or_io : String | IO) from_json, from_yaml(string_or_io : String | IO) from_yaml

### Macros inherited from class `Object`

class_getter(*names, &block) class_getter, class_getter!(*names) class_getter!, class_getter?(*names, &block) class_getter?, class_property(*names, &block) class_property, class_property!(*names) class_property!, class_property?(*names, &block) class_property?, class_setter(*names) class_setter, def_clone def_clone, def_equals(*fields) def_equals, def_equals_and_hash(*fields) def_equals_and_hash, def_hash(*fields) def_hash, delegate(*methods, to object) delegate, forward_missing_to(delegate) forward_missing_to, getter(*names, &block) getter, getter!(*names) getter!, getter?(*names, &block) getter?, property(*names, &block) property, property!(*names) property!, property?(*names, &block) property?, setter(*names) setter

##
Constructor Detail

def self.new(ctx : YAML::ParseContext, node : YAML::Nodes::Node) #
def self.new(pull : JSON::PullParser) #
def self.new #

##
Class Method Detail

def self.from_json_object_key?(key : String) #

##
Instance Method Detail

def initialize #