From: Austin Ziegler <halostatue@...>
Date: 2005-12-30T03:19:33+09:00
Subject: Re: What is the difference between :foo and "foo" ?

On 29/12/05, Steve Litt <slitt@earthlink.net> wrote:
> On Thursday 29 December 2005 11:20 am, Kirk Haines wrote:
>> On Thursday 29 December 2005 8:45 am, Steve Litt wrote:
>>> They wouldn't exist, or they wouldn't be called symbols. If I'm
>>> referring to an instance instead of a value, I could call it
>>> &variable as in C, or I could call it :variable, but in that case
>>> I'd call it a reference, not a symbol.
>> It's not a reference. Symbols are much simpler than that. Really.
>> They are just an integer with some sequence of characters to
>> represent it, all wrapped up in an object.
> OK, let me see if I'm correctly understanding you.
>
> :wilbur is an object. That object has two properties, which one could
> call, in generic and not Ruby terms, a key and a value. The key is an
> integer. The value is "wilbur". Neither the key nor the value can be
> changed during the execution of the program. When we write:

No. :wilbur is an object. It has *one* property, itself. You can ask for
integer or string representations, but :wilbur's value is :wilbur and
there will only ever be one :wilbur.

> attr_accessor :wilbur
>
> what really happens is that the function attr_accessor() takes symbol
> :wilbur as an argument, tacks on a @ to the string's value in order to
> make the true class variable @wilbur, and then writes a tiny get and
> set functions whose names are wilbur, such that:

Sort of. In the link that I posted for you earlier, you'll note that I
wrote an accessor generator (md5_accessor) which can be used to create
accessors that deal with variables named completely differently than the
accessors.

The method Module#attr_accessor will take the symbol and use it as a
name to create accessors (#wilbur and #wilbur=) that *coincidentally*
work on a variable of the same name. It doesn't *create* that variable.

> my_object.wilbur = 22
> puts my_object.wilbur
>
> So my initial comment that it seemed like magic is true only to the
> extent that the "magic" performed by attr_accessor is to create the
> set and get methods with the same name as the symbol that is its
> argument.

You are correct in this last. The "magic" is in attr_accessor, not in
the Symbol. The Symbol is just a name.

-austin
--
Austin Ziegler * halostatue@gmail.com
               * Alternate: austin@halostatue.ca