Returns an array holding the items of 'arr' mapped through ob->fun(). The function 'fun' in 'ob' is called for each element in 'arr' with that element as parameter. A second parameter 'extra' is sent in each call if given. Principal function:
foreach (index) arr[index] = ob->fun(arr[index],extra);
The value returned by ob->fun(arr[.index.], extra) replaces the existing element in the array.