Region.size

alias R = Region!(int, int);
alias TI = R.TaggedInterval;

R emptyRegion;
auto region1 = R(0, 0, 10);
auto region2 = R([TI(0, 0, 10), TI(0, 20, 30)]);
auto region3 = R([TI(0, 0, 20), TI(0, 10, 30)]);

assert(emptyRegion.size == 0);
assert(region1.size == 10);
assert(region2.size == 20);
assert(region3.size == 30);