isArray

// check is_index
   import std.conv : to;

   uint index;
   assert(is_index("0", index));
   assert(index is 0);
   assert(!is_index("-1", index));
   assert(is_index(uint.max.to!string, index));
   assert(index is uint.max);

   assert(!is_index(((cast(ulong) uint.max) + 1).to!string, index));

   assert(is_index("42", index));
   assert(index is 42);

   assert(!is_index("0x0", index));
   assert(!is_index("00", index));
   assert(!is_index("01", index));

   assert(is_index("7", index));
   assert(index is 7);
   assert(is_index("69", index));
   assert(index is 69);