Bob Ippolito wrote:
> On May 29, 2004, at 1:06 PM, Raymond Hettinger wrote:
>
>> Instances of classes inheriting from str, tuple, etc cannot be weakly
>> referenced. Does anyone know the reason for this?
>
>
> They can not accept non-empty __slots__ either, which is probably closer
> to the source of the problem. I have no idea what the reason is. I
> imagine it's something to do with optimization, and/or because they are
> immutable.
it is because they are var-sized objects. There is no place
to put the weakref pointer in, since the variable part
starts right at the beginning of the object.
This is not really necessary, because strings are not so
var-sized at all. After creation, they are fixed sized,
and we could implement special cases for all such types,
similar to what I did with type objects and slots.
The property of "var-sized" objects is everything else but
being var-sized. They are fixed sized after initialization,
just that you cannot have fixed offsets at "compile time".
The real var-sized objects are fixed-size :-)) , because they
use an extra memory area to grow or shrink at runtime.
I think slots could be added to all var-sized objects, and
weakref is nothing else but kind of slot. The cost would be
a little more computation and some special macro which points
to the area "behind" the object. See my special case for
meta types in Stackless typeobject.c.
ciao - chris
--
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