Am 05.06.2013 22:01, schrieb Kapps:
On Tuesday, 4 June 2013 at 04:07:10 UTC, Andrei Alexandrescu wrote:
Choosing virtual (or not) by default may be dubbed a mistake only in a
context. With the notable exception of C#, modern languages aim for
flexibility and then do their best to obtain performance. In the
context of D in particular, there are arguments for the default going
either way. If I were designing D from scratch it may even make sense
to e.g. force a choice while offering no default whatsoever.
C# chose final-by-default not simply because of performance issues but
because of issues with incorrect code. While performance is an issue
(much more so in D than in C#), they can work around that using their
JIT compiler, just like HotSpot does for Java. The real issue is that
overriding methods that the author did not think about being overridden
is *wrong*. It leads to incorrect code. Making methods virtual relies on
some implementation details being fixed, such as whether to call fields
or properties. Many people who wrap fields in properties use the fields
still in various places in the class. Now someone overrides the
property, and finds that it either makes no change or in one or it works
everywhere except in one or two fields where the author refers to the
field. By forcing the author to specifically make things virtual you
force them to recognize that they should or shouldn't be using the
property vs the field. There are many other examples for similar issues,
but I feel properties are one of the biggest issues with
virtual-by-default, both from a correctness standpoint and a performance
standpoint. Having @property imply final seems rather hackish though
perhaps.
Anders Hejlsberg talks about why they decided to use final by default in
C# at http://www.artima.com/intv/nonvirtualP.html. See the Non-Virtual
is the Default section. They do this *because* they saw the drawbacks of
Java's virtual by default and were able to learn from it.
Oh, I though it was based on his experience with Object Pascal and
Delphi, that also do final by default.
Thanks for sharing.
--
Paulo
