Re: Garbage collector on Ada?

["Robert I. Eachus" <rieachus@attbi.com>]

Dr. Michael Paus wrote:

> Just for curiosity. Has there ever been an Ada implementation besides 
> JGNAT which uses a garbage collector?
 

Yes, Symbolics had an Ada 83 compiler with garbage collection.


Pedro Menendez wrote:

 
> Since the standard specifically allows garbage collectors,
> it would be very strange if it was impossible to implement.
> But it definitely appears to be atypical.


Actually, the reason that most Ada compilers don't have general garbage 
collectors is that most of Ada is designed to avoid distributed costs. 
For example, if you use Ada.Strings.Unbounded, the standard requires 
that the type not leave uncollected garbage. The typical implementation 
is to use a protocol that either explicitly does reference counting or 
does copying on assignment.  That way you only pay a small, fixed cost 
if and when you use Ada.Strings.Unbounded.

Similarly most packages that create either many objects on the heap or 
large objects on the heap tend to take out their own garbage.  It would 
be nice to have a general purpose garbage collector available as a 
storage pool, such that any objects in the pool would be subject to 
garbage collection.  But I don't know of such an implementation.