Am 14.02.2021 um 19:07 schrieb Ryan Joseph via fpc-pascal:
On Feb 14, 2021, at 9:55 AM, Sven Barth via fpc-pascal
<fpc-pascal@lists.freepascal.org> wrote:
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).
Remind me again, what happens when you cast a class to an interface? It's a
runtime check with GetInterfaceByEntry?
It's a runtime conversion, but normally you don't do the conversion for
every method call, but instead cache the interface (or work solely with
the interface), thus the performance impact through the conversion
amortizes (and again, there's so memory allocation by the conversion
itself, of course if the interface getter in case of a interface
delegation does a lazy initialization that's different, but the
conversion itself does not require an allocation).
Regards,
Sven
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