我应该在Ruby on Rails中使用引号或冒号作为会话密钥吗？

Question

Currently I have a session variable that returns the same value when I use both session["test"] or session[:test] . Are these two the same? Is it better to use one over the other?

Thanks

Answer 1

In a standard Ruby Hash they're not the same ( string vs symbol )

However, the rails SessionHash subclass calls to_s on the keys before storing them, so all keys are stored as strings (even if you specify a symbol):

class SessionHash < Hash

  def [](key)
    load_for_read!
    super(key.to_s)
  end

  def []=(key, value)
    load_for_write!
    super(key.to_s, value)
  end

That's why session[:test] and session["test"] will return the same value in rails.

Answer 2

As far as ruby string and symbols go they are not the same.

As a general rule, you should use the second form, a symbol is something used to represent something which would otherwise be a string. It is a way to efficiently have descriptive names while saving the space you would use to generate a string multiple times.

This means that you do not create a new instance each time you refer to the symbol as you would a string. The symbol is simply a better way to represent the value you are describing.

Just for completeness, I should mention a symbol can trivially be converted to a string if you need a representation later.

if you want to read more there is a lengthy blog post just here which explains ruby symbols well. Suffice to say they are an optimisation.

That said ruby SessionHash calls to_s on symbols so you can use either in this case as a string will result from the input either way.

Answer 3

No, they aren't precisely the same. They're two ways of accomplishing the same thing.

In general, in Ruby a major use of symbols is as keys. Symbols are :these_things . Hash keys are a typical use for them...

{
  :name => 'Mary',
  :rank => 'Captain'
}

Session keys are also usually symbols.

Using Strings instead won't hurt anything, but symbols are more typical.