flatten.rb

def foo(x)
  a = x.flat_map(&:bar)
  (a + [1]).flatten
end

def foo2(x)
  a = x.flat_map(&:bar)
  a + [1]
end

X = Struct.new(:bar)
x = [X.new([[:x]])]

p foo(x) # => [:x, 1]

p foo2(x) # => [[:x], 1]