Question

The Phobos documentation shows the following example of ranges passed to a variadic function

int[] a = [ 1, 2, 4, 5, 7, 9 ];
int[] b = [ 0, 1, 2, 4, 7, 8 ];
int[] c = [ 0, 1, 4, 5, 7, 8 ];
assert(equal(setIntersection(a, a), a));
assert(equal(setIntersection(a, b), [1, 2, 4, 7][]));
assert(equal(setIntersection(a, b, c), [1, 4, 7][]));

But what if you have a range of ranges, and you don’t know in advance how many elements it will contain, like

int[][] a = [[1,2,3,4],[1,2,4,5],[1,3,4,5]];

The only thing I can think of is

if (a.length > 1) {
    auto res = array(setIntersection(a[0], a[1]));
    for (int i = 2; i < a.length; i++)
        res = array(setIntersection(res, a[i]));
    writeln(res);
}

Which works. But I was hoping to be able to pass the argument directly to the function, like setIntersection(a.tupleof) or something like that (I know that tupleof doesn’t work here).

Answer 1

if you don’t know how many elements a will have you won’t be able to expand it into a tuple at compile time (and consequently pass it into a function)

so that for loop is your best bet (or implement your own setIntersection that can take a range of ranges)