* @param source Source host
* @param dst Destination host
*/
-using SmpiOpCostCb = std::function<double(double size, simgrid::s4u::Host* source, simgrid::s4u::Host* dst)>;
+using SmpiOpCostCb = std::function<double(size_t size, simgrid::s4u::Host* source, simgrid::s4u::Host* dst)>;
/** @brief SMPI functions that accept cost functions */
enum class SmpiOperation { RECV = 2, SEND = 1, ISEND = 0 };
/**