On 10/31/10 3:38 AM, Dmitry Olshansky wrote:
On 31.10.2010 6:56, Andrei Alexandrescu wrote:
[snip]
Walter and I discussed the matter again today and we're on the brink
of deciding that cheap copy construction is to be assumed. This
simplifies the language and the library a great deal, and makes it
perfectly good for 95% of the cases. For a minority of types, code
would need to go through extra hoops (e.g. COW, refcounting) to be
compliant.
I'm looking for more feedback from the larger D community. This is a
very important decision that marks one of the largest departures from
the C++ style. Taking the wrong turn here could alienate many
programmers coming from C++.
So, everybody - this is really the time to speak up or forever be silent.
Andrei
The only things I've ever seen in C++ _correctly_ using _costly_ copy
constructor are containers and some bignums, but then most of the time
one need to define swap for it to perform well in the std::sort for
instance, and that is oftentimes forgotten.
That indicates that containers are better off being reference types,
which is what they are in D anyway, and bignums I do belive could use
COW/small number optimization.
I'd go with cheap constructors assumed given that it simplifies matters
a lot.
I've been thinking of this too - costly copy construction requires
constant attention in client and library code alike (e.g. STL
containers) or is flat out in bad taste (e.g. the mythical Matrix class
that returns copies from operators).
Andrei
