Re: Really more GC talk (was: Reading a line of arbitrary length)

[fjh@murlibobo.cs.mu.OZ.AU (Fergus Henderson)]

dewar@merv.cs.nyu.edu (Robert Dewar) writes:

>Fergus said
>
><<The standard implies that standard-conforming implementations can use
>only conservative garbage collection, and that implementations that use
>non-conservative GC techniques cannot be standard-conforming.
>
>That still seems to me to be a potentially undesirable constraint to
>place on standard-conforming implementations.
>>>
>
>I can't figure out the strange misreading of the RM that leads to this
>incorrect conclusion, but it is certainly an incorrect conclusion.
>There is no such constraint in the RM.

Suppose I pass an Ada access type to a C function and store the pointer
in a C global variable, and suppose that the data pointed to is
reachable only via that pointer.  Can my combined C/Ada program be
standard-conforming?  If not, then I guess I'll just have to give
up mixed-language programming.  If so, then does the Ada standard allow
the implementation to reclaim the memory?  If so, please cite chapter
and verse.  If not, then this would place potentially undesirable
constraints on implementations.  In particular, it would prohibit
non-conservative GC techniques -- or require them to non-conservatively
collect the C code too, which is not feasible, due to the presence of
undiscriminated unions.

--
Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3         |     -- the last words of T. S. Garp.