def foo(n)
  if n.respond_to?(:times)
    n.times {|_| n = :sym }
  elsif n.respond_to?(:+)
    n + "foo"
  else
    n & false
  end
end


foo(1)
foo("str")
foo(true)

# no error expected

__END__
# Classes
class Object
  private
  def foo: (Integer | String | true n) -> (Integer | String | bool)
end