responds_to.rb

def responds_to?(method_name)
  ->(obj) { obj.respond_to?(method_name) }
end

[
  1,
  "string",
  %w{an array},
  {a: 'hash'}
].each do |object|
  case object
  when String, Integer
    puts object
  when responds_to?(:join)
    puts object.join(' ')
  else
    puts object.inspect
  end
end