On 07/27/12 21:22, Stuart wrote:
> On Friday, 27 July 2012 at 19:17:10 UTC, H. S. Teoh wrote:
>>
>> Nevertheless, D has gotten to the point where it's powerful enough that most
>> feature requests can be implemented in a
>> library rather than as a language extension.
>
> How could Yield be implemented as a library feature? Something like:
>
> return ITERATOR(
> { ...setup code ... },
> { ...loop body code... })
>
> ?
>
> I don't see how that would work.
The threading "yield" and the iterator "yield" are actually strongly related.
By yielding a coroutine, you can effectively suspend a routine
and resume it later. Let me give you an example:
int delegate() genEvenNumbers() {
// not actual api
return startCoroutineIterator!int((void delegate(int) yield) {
for (int i = 0; true; i++) if (i % 2 == 0) yield(i);
});
}
// long form of the above function, so you can see how you gain iterator-style
behavior via coroutines
int delegate() genEvenNumbers() {
int* resultp = new int;
void cofun(void delegate(int) yield) {
for (int i = 0; true; i++) if (i % 2 == 0) yield(i);
}
// still not actual api
auto coroutine = new Coroutine(1024*1024 /* stack size */);
// set the 'main function' of the coroutine
coroutine.fun = {
// yield, when called, will cause the coroutine to suspend and run() to
return
cofun((int i) { *resultp = i; coroutine.yield(); });
};
// run the coroutine up to the next yield, then return yielded value
return { coroutine.run(); return *resultp; };
}
You can fully implement Coroutine as a library, provided you're somewhat
confident with x86 assembly and stack frame layouts.
