Re: speed of generic code in Ada (vs Java)

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wccy7633br3.fsf@shell01.TheWorld.com...
> Graham <graham.stark@virtual-worlds.biz> writes:
>
>> In any case, the 5x comparison sounds extreme and probably comes from
>> comparing arrays of ints with something from the Java Collection
>> classes, which is a bit like comparing Ada arrays with Ada Containers.
>
> I don't see why.  Ada.Containers.Vectors, for example, does not
> introduce an extra level of indirection for each component of the
> vector.  Ada is more like C++ in that regard.

Sorry, but there is no language guarentee of this; it's more that an 
implementation of Ada.Containers.Vectors does not *have* to have a extra 
level of indirection. For Janus/Ada, for  instance, there would be such an 
(implicit) indirection coming from the generic code sharing even if there 
isn't any explicit one.

And I'd still expect comparisons to be slower, because the "=" code probably 
is a loop doing element comparisons (it has to use the formal "=" operator 
and cannot assume that the actual is the predefined "="). It might be 
possible for a compiler to optimize that, but it would be pretty complex to 
do so. (And even "=" for integers has to be done in a loop on some 
targets -- a bit comparison is not accurate for 1's complement machines, for 
instance.)

The net effect is that generalizations about Ada performance are probably 
not well-founded. Usually, Ada performance is similar to that of C++, but 
implementation differences can be a big deal and more different than those 
between languages.

                                 Randy.