At 09:57 PM 4/11/00, Lex Spoon wrote:
>"R. A. Harmon" <harmonra at webname.com> wrote:
>
>> I am trying to implement an ANSI conforming #=.  As I understand it, #abc
>> (an instance of class Symbol) = 'abc' (an instance of class String) would be
>> non-conforming implementation as their classes are different.
>> 
>
>Apparently it's ambiguous.  Allen Wirfs-Brock gave a pretty good
>argument earlier today.

As I read his explanation the ANSI Standard is not ambiguous, it just allows
various implementation.  The SequenceableCollection >> #= specification:

Refinement: <sequenceReadableCollection>
Unless specifically refined, the receiver and operand are equivalent if all
of the following are true:

        1. The receiver and operand are instances of the same class.
        2. They answer the same value for the #size message.
        3. For all indices of the receiver, the element in the receiver at a
                given index is equivalent to the element in operand at the
                same index.

means same class when it says same class.


>So we can choose whichever way we like, and just remember that if we
>want to write portable Smalltalk code, we can't rely on it working one
>way or the other.  :(

--- Allen Wirfs-Brock:

The ANSI Standard was trying to allow for this possibility. I think it 
succeeded in allowing this.

Java also essentially takes the above approach. There is only a single 
String class. The intern() method of a String returns a unique "canonical" 
instance of the String that corresponds to the receiver.  Thus such a 
canonical string has essentially the same semantics as a Smalltalk Symbol 
but only a single class is used to represent both canonical and 
non-canonical strings.

---

Badly simplified, we can choose to implement String and Symbol as a single
class, say StringSymbol, used to represent both and only then would:

        #abc (an instance of class StringSymbol)
                = 'abc' (an instance of class StringSymbol) -> true

As I read it there are other possible variations in implementation.

--
Richard A. Harmon          "The only good zombie is a dead zombie"
harmonra at webname.com           E. G. McCarthy
Spencer, Iowa