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Wed Aug 5 13:54:45 CEST 2009

Representing constants

I might be useful to make it possible to directly cast non-managed
objects, by assuming the class pointer is in the slot _before_ the
pointer.  It is upto the user then to _never_ place them inside GC
managed vectors, as they won't have a valid class pointer.

Elaborate on this a bit..

I.e. it would be nice for a (const char *) to be a valid object that
can reside in a collected data structure.  I.e. the object itself
should be recognizable as not requiring free().

The problem then is that I'm running out of tags:

00 non-managed pointer
01 vector
10 integer
11 bool

Using more than 2 tag bits places extra contstraints on pointer
alignment.  Booleans are useful for predicate implementation in
Scheme.

It is possible however to use the 01 vector slot, since we know what
that will point to:
     - integer (it's a live vector, and the int = size)
     - vector  (moved object)

This could be a non-managed pointer to represent a class?

Maybe another workaround is simpler: doubly wrapping all predicates
and representing bools as integers.

Let's stick to what we have and thing about this a bit more.. It looks
like bools are more useful than constants.  

Otoh: since bools require only two values, and are actually constants,
the problem is solved:


00 constant = non-managed pointer
01 vector
10 integer
11 managed pointer


Let's implement this first before rewriting everything to primitives.



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