Re: C to Ada : a piece of code

[geert@fozzie.sun3.iaf.nl (Geert Bosch)]

Robert Dewar (dewar@cs.nyu.edu) wrote:
`` In most cases, this extra subtraction ends up being essentially free since
   it is always pulled out of loops. In any case, it is perfectly possible
   to have implementations that avoid this subtraction all the time by using
   virtual origins. ''

Please, don't do this! It is possible, but certainly not perfect!  If
applications are long-lived and they dynamically allocate memory at a
certain rate, garbage collection is necessary for keeping the language
safe.

Since Ada-compilers do not provide garbage collection (sad, but still
true), users depend on being able to add a conservative garbage
collector.  Conservative garbage collectors depend on pointers to
objects be stored in a fixed format. Having virtual origins breaks all
conservative garbage collectors and makes it almost impossible for a
third party to add garbage collection to the compiler.

Not being able to write safe applications using dynamically allocated
memory ('global memory objects' might be a better term) is a very
high price to pay for such a tiny performance improvement. 

Of course I'm not biased by the fact that I do have an experimental
garbage collector for GNAT at home ;-)

Regards,
   Geert
-- 
E-Mail: geert@sun3.iaf.nl    
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