Michel Fortin Wrote:
Le 27-juin-2013 à 18:35, Michel Fortin a écrit :
> class MyObject
> {
> // user-implemented
> static void opRetain(MyObject var); // must accept null
> static void opRelease(MyObject var); // must accept null
>
> // optional (showing default implementation below)
> // this can be made faster with for some implementations of
ref-counting
> // only call it for an assignment, not for
constructing/destructing the pointer
> // (notably for Objective-C)
> static void opPtrAssign(ref MyObject var, MyObject newVal) {
> opRetain(newVal);
> opRelease(var);
> var = newVal;
> }
> }
>
> This maps 1 on 1 to the underlying functions for Objective-C ARC.
Actually, I made a small error in opRetain. To match Objective-C ARC it should
return the retained object:
static MyObject opRetain(MyObject var); // must accept null
and the default implementation for opPtrAssign would then become:
static void opPtrAssign(ref MyObject var, MyObject newVal) {
newVal = opRetain(newVal);
opRelease(var);
var = newVal;
}
One reason is that Objective-C blocks (equivalent of delegate literals) are
stack allocated. If you call retain on a block, it'll make a copy on the heap
and return that copy.
Another reason for opRetain to return the object is to enable tail-call
optimization for cases like this one:
NSObject x;
NSObject getX() {
return x; // D ARC should insert an implicit opRetain here
}
Of course it doesn't necessarily need to work that way, but it'd certainly make
it easier to integrate with Objective-C if it worked that way.
