On 10/31/10 8:04 AM, Michel Fortin wrote:
On 2010-10-30 23:56:24 -0400, Andrei Alexandrescu
<[email protected]> said:
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.
A simple question: can a reference counter work with const and immutable?
const(S) func(ref const(S) s) {
return s; // this should increment the reference counter, but can we
bypass const?
}
Bypassing const/immutable could work, but if your data is immutable and
resides in read-only memory you'll get a crash.
There are several solutions possible, some that require the compiler
knowing about the idiom, and some relying on trusted code. One in the
latter category is to create immutable objects with an unattainable
reference count (e.g. size_t.max) and then incrementing the reference
count only if it's not equal to that value. That adds one more test for
code that copies const object, but I think it's acceptable.
Andrei
