From: "David A. Black" <dblack@...>
Date: 2008-01-28T20:57:57+09:00
Subject: Re: Symbol#empty? ?

Hi --

On Mon, 28 Jan 2008, Dave Thomas wrote:

>
> On Jan 28, 2008, at 12:48 AM, Gary Wright wrote:
>
>> In the most abstract sense, symbols map from string equality to object 
>> identity.  This provides a mechanism for accessing uniquely named objects 
>> regardless of how you came by the name:
>>
>>   literal    :foobar
>>   dynamic    str.to_sym
>>   computed   (str1 + str2).to_sym
>
> OK, but why do we need this?
>
> Symbol tables are fundamentally an optimization: a way of looking up an 
> identifier. That's why the predominant use of symbols in Ruby (post Rails) is 
> as hash keys, where they serve the same function. What function does 
> :"a<space>b" serve for Ruby programmers?(*) And is the benefit of having it 
> worth the inconsistencies and security issues involved.
>
> Why not instead say that Symbol is for representing symbols, and have #intern 
> complain if the corresponding strings isn't valid? That would allow 
> :"+(binary)" to make sense, as the underlying symbol is the same as :+.  And 
> then if some application in future has an obscure need to represent the works 
> of Shakespeare as a symbol, they can simply use a hash like everyone else 
> would... :)

It's hard to specify what a valid symbol is, though -- not just
because of the new string-like behaviors, but because symbols get put
in the table even if they're not valid identifiers.  Here's a 1.8.6
demo:

>> s = Symbol.all_symbols; 1
=> 1
>> class C; define_method("good morning, everyone!") {}; end
=> #<Proc:0x00000000@(irb):2>
>> t = Symbol.all_symbols; 1
=> 1
>> t - s
=> [:C, :"good morning, everyone!"]
>> Object.new.send("this will be put in the sym table")
NoMethodError: undefined method `this will be put in the sym table'
for #<Object:0x31bc30>
         from (irb):5:in `send'
         from (irb):5
>> u = Symbol.all_symbols; 1
=> 1
>> u - t
=> [:u, :"this will be put in the sym table"]

I tend to agree about the hybrid nature of symbols in 1.9. I don't
know why one would ever need to do a swapcase operation on a symbol,
for example (though there could of course be use cases I'm not
thinking of).


David

--
David A. Black
Director, Ruby Power and Light, LLC
Ruby/Rails training and consulting
http://www.rubypal.com