unions.cr

struct Block
  def initialize(str : String)
    @data = str
  end

  def initialize(int : Int32)
    @data = int
  end

  def data
    @data
  end
end

# So @data is String | Int32, a union

str_block = Block.new "Hello"
int_block = Block.new 1

p str_block.data #=> "Hello"
p int_block.data #=> 1

# You can't invoke a method on data if it's not on all types
# str_block.data.length #=> undefined method 'length' for Int32
# str_block.data.abs    #=> undefined method 'abs' for String

data = str_block.data
case data
when String
  puts "Data is a string: #{data}"
when Int32
  puts "Data is an int: #{data}"
end