From: Markus <markus@...>
Date: 2004-09-20T12:27:39+09:00
Subject: Re: Nuby question about symbols


I'll give it a shot:

      * Symbols are an idea borrowed from lisp.  They are immutable,
        atomic, named, globally unique values with an efficient internal
        storage.
              * immutable, like (say) nil or an integer, in that you
                can't change them, give them new values, update them,
                etc.
              * atomic in that you can't "take apart" a symbol or "peek
                inside it" like you can with a string
              * named, in that each symbol has a human-readable form
                (unlike, say, pointers)
              * globally unique in that if a symbol is referenced
                anywhere in the program it is the same object that the
                same reference would get you anywhere else.  This is the
                same way integers work (7 is 7, no matter where it
                occurs in the program), but unlike how arrays and
                strings work (you can, for example, have the string
                "seven" in several places in your program, and they are
                NOT the same object).
              * efficient in that they are usually implemented as
                something like an integer or a pointer, and thus are
                quick to compare, small to store, etc.
      * Symbols are used wherever they are useful.
              * Symbols fill a roll in ruby (and in lisp) something like
                enumerated types in pascal--in fact, if you single
                imagined a pre-existing enumerated type containing all
                possible values, that would work sort of like symbols.
              * Symbols can be used for arbitrary state or condition
                labels (e.g. :male/:female, :jan, :feb, :mar...,
                :on,:off,:standby,:out_of_service,... :reverse,:neutral,
                :first,:second,:third,:overdrive etc.)
              * Symbols can be used as "exceptional" values (e.g.
                :not_a_number, :to_be_determined, etc.) much as nil or
                -1 often are, but in a way that is much easier to read. 
                They are much more efficient than strings, which are
                often also used in such contexts

If that doesn't help, let me know and I'll try to dredge up some online
references--or you can always google.

-- MarkusQ  


On Sun, 2004-09-19 at 18:50, Felipe Malta de Oliveira wrote:
> In spite of the recent comments stating that newbies should not be afraid to
> post silly questions, I now ask...
> 
> Could anybody give me a little knowledge about symbols? Like what they are,
> why and where they're used and such...Or give me a pointer to somewhere I
> can find that information?
> 
> Thanks a lot,
> 
> Felipe
>