Am 14.02.2021 um 13:30 schrieb Michael Van Canneyt via fpc-pascal:
On Sun, 14 Feb 2021, Sven Barth via fpc-pascal wrote:
So whether it be this, or just an improvement on the Interfaces we
already have, I'd definitely personally be in favor of something
that "works like Interfaces except minus the negative performance
implications."
There are no significant performance implications of interfaces.
They're essentially a virtual method call, something that one is
doing all day long with Object Pascal classes.
I think the "performance implications" is more referring to memory
management.
Interfaces means an extra object per interface, so more objects on the
heap with all the extra memory management that implies.
No, interfaces by *themselves* don't mean that. An interface instance is
merely a shifted Self pointer that points to the static VMT of which the
entries correct the Self pointer again upon the method call. This can be
seen in GetInterfaceByEntry in rtl/inc/objpas.inc (the core function
dealing with the casting of class to interface).
That is why I think that a 'trait' using an object/advanced record has
it's advantage: There is only 1 continuous memory block for a class
implementing
traits.
For delegation it is true that memory allocation is involved, but let's
be fair here: this instance is normally allocated together with its
parent instance and thus the performance impact only adds to the already
costly instantiation of the parent instance. And if you really need to
worry about heap fragmentation then you have other problems in my opinion...
That said, as I wrote, one could in principle allow the use of records
and objects for the delegation as well, after all delegation classes
don't need to implement the interface either and the compiler needs to
create appropriate thunks anyway.
Regards,
Sven
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