class clock :
Its provides the most precise time that the underlying OS can achieve (generally microseconds or nanoseconds). It also ensures monotonicity, which means that the returned time can never go backward, even if the system time is changed.
The time value returned by the clock can then be converted to a number of seconds, milliseconds or even microseconds.
let clock;= new clock in
let time1 = clock#get_elapsed_time in
let time2 = clock#restart in
method destroy :
method get_elapsed_time :
method restart :