more radical change?

[Stephen Weeks]

> The difficulties we have currently are all caused by the fact that references
> to  objects  are NOT the same as pointers to the first word used by an object
> in the heap.  This could be changed.  The only disadvantages  I  see  to  the
> change are:
> 
>     Getting  to  the  data associated with an object would involve a slightly
>         larger offset from the reference.  For array  subscript  calculations
>         it would mean that the address of X[i] would be
>             X + offset + i * size-of-element
>         where  offset is the number of bytes from the first word of the array
>         object to the first first word of data.
> 
>         I don't think that this is important.

Simpler array subscript calculations was one of the reasons we chose
the scheme we did.  I don't agree with your statement that the extra
offset is not important, and need to be convinced.

>     The mutator code would now be more intimately involved with heap  layout.
>         Currently  it  only  knows  when it is creating an object, but now it
>         would also have to know when it is accessing  an  object.   It  would
>         have to know about header words and the like.
> 
>         This could be a serious objection if we go to some fancy generational
>         GC where one might want to use some kind of BBOP for small objects.

This is another good objection to the change.