On 13 March 2012 19:25, Andrei Alexandrescu <SeeWebsiteForEmail@erdani.org> wrote:
On 3/13/12 12:02 PM, Manu wrote:
There's a few finicky differences. I'm still of the understanding (and I
may be wrong, still mystified by some of D's more complicated template
syntax) that once you give the returned tuple a name, it is structurally
bound to the stack. At that point, passing any member by-ref to any
function must conservatively commit the entire tuple to the stack. This
behaviour won't be intuitive to most users, and can be easily avoided;
by obscuring the Tuple from user visibility, they can only access the
returned values through their independant output assignments, which
guarantees the independence of each returned item.
I don't see how? I'm just saying that I don't think they are pragmatically identical.
Syntactically, scatter can't declare new variables inline (?), it also
uses additional lines of code (1 + as many variables as you need to
declare), which is very disruptive to flow.
What value does it add over Kenji's change? Is this because Kenji's change is unable to perform direct to existing variables?
My understanding from early in the thread was that Kenji's change hides the returned tuple, and performs a convenient unpack. How can you perform a scatter if the tuple instance is no longer visible?
What people want from MRV is to capture the returned
values independently. If I /wanted/ to capture the returned Tuple (the
extremely rare case), I'd rather do that explicitly, something like this:
auto t = tuple(mrvFunc());
No. Tuple stays together by default and is expanded explicitly. This is not negotiable.
Then I think you commit to polluting the common case with wordy redundant noise. Why is it so important?
If it were expanded by default, all you need to do it put a tuple constructor around it to wrap it up again.
It creates semantic multi-assignment problems I suspect? This is what I reckon needs to be addressed to make the implementation really nice.
scatter/gather is nice and simple, I'll take it in the mean time, but I
think it would be a shame for it to stop there longer term...
That said though, it's all still nothing to me without at least a
promise on the ABI :) .. And I feel that should ideally come in the form
of a language policy/promise that this feature will be 'efficient' (or
at very least, not /inefficient/ as it is now), and leave it to compiler
implementations to concur with that promise, ie, failing to be
'standards' compliant if they fail to do so.
This is not for me to promise.
Sure, but it'd be good to get a weigh in on that issue from Walter, and others, Iain?