respond_convert.rb

def _?(o, method, &block)
  o.respond_to?(method) ? o : block.call(o)
end

def eachize(one_or_more)
  _?(one_or_more, :each) { |o| [o] }
end

def foo(one_or_more)
  eachize(one_or_more).each do |o|
    puts o
  end
end

foo(3)
# 3

foo([1,2])
# 1
# 2