import std.range : iota;
// 0 1 2 3 4 5
auto sl = iota(5);
size_t index = sl.findIndex!"a == 3";

assert(index == 3);
assert(sl[index] == 3);

assert(sl.findIndex!(a => a == 8) == size_t.max);

import mir.ndslice.topology : iota;
// 0 1 2
// 3 4 5
auto sl = iota(2, 3);
size_t[2] index = sl.findIndex!(a => a == 3);

assert(sl[index] == 3);

index = sl.findIndex!"a == 6";
assert(index[0] == size_t.max);
assert(index[1] == size_t.max);