From: Jim Weirich <jim@...>
Date: 2005-01-20T04:34:48+09:00
Subject: Re: value by reference


trans. said:
> Personally, I've alwasy thought of variables as containters,

A perfectly good way to think of variables in FORTRAN, Ada, Pascal,
Eiffel, C, C++, C#, Java, FORTH and Algol.  In these languages variables
are containers into which you put values (I call this the shoebox model of
variables).

However, it is misleading in Python, Lisp, Scheme and, of course, Ruby. 
In these languages, thinking of assignment as binding (associating) a name
to a value is more productive in that you can reason about the language
purely in terms of objects and names associated with objects.  No need to
introduce the concept of references.  And the difference between immediate
objects and reference objects (almost[1]) melts away.

For more thoughts on this, see:
http://onestepback.org/index.cgi/Tech/Ruby/Shoeboxes.rdoc.  For an example
of "breaking" the rules and re-introducing references in the mix, see:
http://onestepback.org/index.cgi/Tech/Ruby/RubyBindings.rdoc.

-- 
-- 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)

[1] Almost, but not quite.  Immediate objects still can't have singleton
methods.