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
true if this union includes the
(Int32 | String).nilable? # => false (Int32 | Nil).nilable? # => true
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