From: Charles Mills <cmills@...>
Date: 2004-07-19T00:18:16+09:00
Subject: Re: DUPSETUP


On Jul 18, 2004, at 12:02 AM, daz wrote:

>
> 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.
>
Thanks for the response.
Can DUPSETUP() be used for objects with type T_DATA?
-Charlie

> 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.
>
> ----------------------------------------------------------------------- 
> -
>
>
>