[Rails] 判斷字串是否為數字

可以直接寫在 initializers 裡面

# [path] string.rb
class String
  def is_number?
    true if Float(self) rescue false
  end
end

Reference

1. http://stackoverflow.com/questions/5654517/in-ruby-on-rails-to-extend-the-string-class-where-should-the-code-be-put-in