From: Sam Roberts <sroberts@...>
Date: 2005-03-19T02:31:58+09:00
Subject: Re: Symbol vs String

Quoting jim@weirichhouse.org, on Sat, Mar 19, 2005 at 12:50:38AM +0900:
> 
> Sam Roberts said:
> > Quoting jim@weirichhouse.org, on Thu, Mar 17, 2005 at 01:36:39PM +0900:
> >> On Wednesday 16 March 2005 09:29 pm, Sam Roberts wrote:
> >> > Quoting jim@weirichhouse.org, on Thu, Mar 17, 2005 at 11:08:59AM
> >> +0900:
> >> > > Use Strings for their content.  Use Symbols for their arbitrary
> >> > > uniqueness.
> >> >
> >> > I used to do this, but ran into problems.
> >> [...]
> >> >   :octet-stream
> >> >
> >> >   NameError: undefined local variable or method `stream' for
> >> main:Object
> >> >           from (irb):3
> >> >   'octet-stream'.intern
> >> >       ==>:"octet-stream"
> >>
> >> Why couldn't you do :octet_stream ?  If your answer is because the dash
> >> comes
> >> from outside ruby, then I would suggest that the content ("_" vs "-") is
> >> important ... indicating that you should use strings.
> >
> > Maybe I don't know what you mean by "arbitrarily unique".
> >
> > "_" vs "-" is no more (or less) important than "a" vs. "z".
> 
> If the choice if symbol names is arbitrary, then I can change the name of
> the symbol everywhere that references it without changing the semantics of
> the program.
> 
> For example, if any of the following choices are equally valid:
> :octetstream, :OctetStream, :octet_stream, :stream_of_octets, :octets,
> :fido, then the choice of name is arbitrary.  Of course, some choices are
> more transparent and convey meaning better, but the program will still
> work even if we call the symbol :xyzzy.  That's what it means to be
> arbitrary.

Ah. Then, no, its not really arbitrary. More specifically, I can make it
arbitrary, but then I might be forced to make it more and more
arbitrary! If I map:

  x-mailer => :xmailer

Then somebody decides to make a header

  xmailer

I have to map:

  xmailer => :zz_xmailer

etc. I guess I could madk a mapping table, hashing strings to
symbols, but at this point symbols aren't making my code clearer or
easier to use.

In the example of mime types, I probably could use abitray symbols.
Anybody who decides to make a new mime type called application/octet_stream or
application/octet_stream given tha application/octet-stream is a
standard name deserves to be publically humiliated. So I could use
:octetstream, arbitrarily.

I just wanted to use symbols for the efficiency, and to emphasize their
uniqueness in terms of case-sensitivity, it seemed to fit, but for
serveral reasons I discovered it didn't.

Cheers,
Sam