Re: limited/non-limited in Ada95

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Jon says

<<There are important cases where this is at _best_ impractical and
actually is more like not _feasible_.  The _view_ for the
implementation should not (can _not_) have limited semantics.  This is
particularly evident when you are constructing GC for Ada _within_ the
language.  Since this is one of Henry's main baileywicks, and since
I've constructed such a GC asset suite _within_ the language, I can
very easily understand where he is coming from.  It's _painfully_
obvious when you have to actually deal with the situation.>>


The view for the implementation most certainly can have limited semantics.
When you are writing garbage collectors, you certainly expect to do some
pretty low level fiddling at the implementation level, where the fact that
the full view is limited is not a problem. But this way you can preserve
the abstraction. I see no problem in writing a GC implementation using
this approach, and in fact we worked out exactly how to do this in the
context of the GNAT project, though no one ever followed through with
an actual implementation, since there has been no demand for GC in GNAT
so far (demand = serious customer willing to pay $)

Robert Dewar
Ada Core Technologies