On Sat, 10 Mar 2012 00:30:05 -0600, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 3/9/12 9:35 PM, Robert Jacques wrote:
On Fri, 09 Mar 2012 22:16:44 -0600, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
On 3/9/12 3:59 PM, Timon Gehr wrote:
Notably, there is no convenient unpacking syntax. Walter does not merge
the patches of Kenji Hara that would fix this because presumably he
fears it could get in the way of a more general solution.
This is because we need to think about that stuff to maximize its
generality.
Was simply applying the unpacking rules to all types (i.e. structs,
classes, etc) ever considered?
How would that work?
Andrei
The proposed unpacking syntax, IIRC, was:
(double a, int b) = fun();
which lowered to:
auto __tup = fun();
double x = __tup[0]; // __tup[0] has a type that is implicitly convertible to
double
int y = __tup[1]; // ditto
Why not instead lower to:
auto __tup = fun();
double x = __tup.tupleof[0];
int y = __tup.tupleof[1];
That way, fun() could return any struct / class, not just a Tuple. For example,
float3 position = { 1.0f, 2.0f, 3.0f };
auto (x1) = position;
auto (x2,y2) = position;
auto (x3,y3,z3) = position;
assert(x1 == x2 && x1 == x3 && x1 == 1);
assert(y2 == y3 && y2 == 2);
assert(z3 == 3);
would be valid. Note that only unpacking a few of the components of a MRV
function is a common practice in my experience (mostly Matlab).
P.S. For unpacking classes / structs directly, i.e.
auto (x3,y3,z3) = position;
should lower to
auto x3 = position.tupleof[0];
auto y3 = position.tupleof[1];
auto z3 = position.tupleof[2];
in order to avoid the extra temporary.
P.S.S. Unpacking should respect protection attributes. Since tupleof doesn't
respect private, protected, etc, the actual lowering should be:
auto __tup = fun();
double x = mixin(__tup.tupleof[0].stringof);
int y = mixin(__tup.tupleof[1].stringof);
