From: ahoward <ahoward@...>
Date: 2002-10-23T06:17:48+09:00
Subject: Re: rb_gc_register_address problem

On Tue, 22 Oct 2002, William Djaja Tjokroaminata wrote:

> I am sorry that 53833 has been replied by 53842 and I don't think 53834 is
> correct.  It seems that rb_gc_mark() does not deal with VALUE* at all, but
> only with VALUE.
>
> In other words, VALUE itself is a pointer (except for the immediate
> object) and all the bit marking and other necessary processes are done on
> the object/data pointed by VALUE.  The VALUE itself may even be changed
> within rb_gc_mark(), but the gc does not actually need &VALUE.

my feeling is that, given a prototype like

  void method (const char const *ptr);

you can be certain the method will change neither the thing pointed at, nor
the ptr itself.

given a prototype like

  void method (VALUE *ptr);

you cannot be sure that, in a current or future release, the ptr itself will
not be changed, since the compiler would allow this behavior.  therefore it
would be a bad idea to rely on the ptr not being changed.  also, i agree that
this was probably a design descision by matz; but since he did NOT write the
prototype as

  void method (const VALUE const ptr);

we may not assume ptr will never be changed.  even if examination of the
source reveals this to be true.

-a


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