From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-05-01T21:07:57+09:00
Subject: Re: def [](v) xx; return yy; end # returned value is ignored !?

At 19:59 01/05/2004 +0900, you wrote:
>On Sat, 01 May 2004 15:28:05 +0900, Jean-Hugues ROBERT wrote:
>
> >>>   - Reference, a reference is an indirect mean of access to a lvalue's
> >>> value that is dereferenced when the value is needed and that also makes
> >>> it possible to assign a value to the lvalue at any time.
>
>There is a problem with treating an lvalue this way, and that is
>that not every lvalue is an storage location.  In fact only
>variables as an lvalue are storage locations, the other ones are
>methods (i.e.: a[]=5 means a.[]=(5), a.foo=bar calls the method
>foo=(bar) on a).

Ruby is cool, a lvalue can be a *method call*.
So when I say "lvalue" I mean Ruby's ones, not the subset that some
other languages provide.

I believe my version of Pointer works with any Ruby valid lvalue:
   a = [1,2,3]
   ptr = Pointer.new{ "a[2]"}
   ptr[] = 4
   p a # => [1,2,4]
See it at end of page http://www.c2.com/cgi/wiki?SinisterSchemeSampleInRuby

>I wouldn't welcome the introduction of references on Ruby,
>because it may mess things up.  Let's say the method "alter"
>takes a reference, and changes the value.  Then calling
>alter(a) will change the value of a, but this is not obvious
>when invoking this method, or look at the code.

I agree that using reference is often a bad thing. I came to
realize that I needed them for some very special code that I
am prototyping. Usually I really don't miss them at all.
But when you need it hard, you miss it hard :-)

>It may be interesting to be able to access variables indirectly
>using binding() (outside eval).
>for example:
>
>a = 2
>binding().local_get(:a)
>=> a == 2

You can !
eval( :a, binding()) ?

>binding().local_set!(:a, 5)
>=> a == 5

eval( "a = 5") or
tmp = arbitrary_expr; eval( "a=tmp", binding())

>And also Binding::ivar_set!, Binding::ivar_get and
>Binding::get_self

eval( "@a", binding)
tmp = expr; eval( "@a = tmp", a_binding)
that_self = eval( "self", a_ binding)

Yours,

Jean-Hugues



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