From: daz <dooby@...10.karoo.co.uk>
Date: 2004-07-18T16:02:16+09:00
Subject: Re: DUPSETUP


Charles Mills wrote:
>
> I was wondering what the purpose of the DUPSETUP() macro is in ruby.h.
> I didn't find anything about it using google.
> What is it intended to be used for?
> -Charlie
>

I guess it may, eventually, be replaced by rb_obj_init_copy
(Object#initialize_copy) referred to in the #dup ri entry [1],
but I'll have a shot at describing what it _was_ for - using
the last remaining example from the source distribution in
array.c:

VALUE
rb_ary_dup(ary)
    VALUE ary;
{
    VALUE dup = rb_ary_new2(RARRAY(ary)->len);

    DUPSETUP(dup, ary);
    MEMCPY(RARRAY(dup)->ptr, RARRAY(ary)->ptr, VALUE, RARRAY(ary)->len);
    RARRAY(dup)->len = RARRAY(ary)->len;
    return dup;
}

"dup" (an empty array with same length) is created (with default state
for a new array and no associated instance variables).

DUPSETUP copies some state flags and any associated instance variables.

MEMCPY copies the object pointers (contents), then the length update
seems to be redundant ( unchanged since rb_ary_new2() ??).


:daz


[1]
------------------------------------------------------------- Object#dup
     obj.dup -> an_object
------------------------------------------------------------------------
     Produces a shallow copy of _obj_---the instance variables of _obj_
     are copied, but not the objects they reference. +dup+ copies the
     tainted state of _obj_. See also the discussion under
     +Object#clone+. In general, +clone+ and +dup+ may have different
     semantics in descendent classes. While +clone+ is used to duplicate
     an object, including its internal state, +dup+ typically uses the
     class of the descendent object to create the new instance.

     This method may have class-specific behavior. If so, that behavior
     will be documented under the #+initialize_copy+ method of the
     class.

------------------------------------------------------------------------