From: Jim Weirich <jim@...>
Date: 2005-03-19T00:50:38+09:00
Subject: Re: Symbol vs String


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.

If the choice of letters is constrained by some outside force, then it is
not arbitrary.  For example, it might come to you as an attribute in an
XML message.  Or perhaps you need to write it to a file, and other
programs expect that exact sequence of strings.  In all these cases, the
content (sequence of letters) is important and cannot be changed without
breaking the program.  When the content of the item is important, use a
string.

-- 
-- Jim Weirich     jim@weirichhouse.org    http://onestepback.org
-----------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct,
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)