On Tuesday 05 February 2008 12:02, Tiziano De Togni wrote:
> Michael Van Canneyt ha scritto:
> >
> > The advantage is mainly that you can have objects on the stack.
>
> sorry, but don't understand exactly what this means exactly.
The main difference is here:
-- 8< --
procedure Uses_Objects;
var
My_Object : tMyObject;
My_Class : tMyClass;
begin
My_Object.Init;
My_Class := tMyClass.Create;
end {Uses_Objects};
-- 8< --
The memory allocation for the class can fail due to resource exhaustion
and also is infinitely slower than the allocation for the object, which
is there as soon as the procedure has been entered. On assembly level,
it is only a different constant that the stack pointer is moved to make
space for the local variables.
Referencing an instance being on the stack may also be a bit faster than
referencing an instance being on the heap, because there's one level of
dereference less, and it may be even more cache-friendly, because the
stack is more likely to be in the cache already than a (newly)
allocated memory block.
Meaning: Memory space and execution speed is more or less known
beforehand and potential memory fragmentation problems are avoided.
Oh, and one thing more: No access violations when referencing an invalid
(not yet initialized) instance. ;)
Vinzent.
_______________________________________________
fpc-pascal maillist - fpc-pascal@lists.freepascal.org
http://lists.freepascal.org/mailman/listinfo/fpc-pascal
