The set of all possible dynamic types (existing types at
run-time, i.e. with a corresponding at_run_time object) which
may be actually returned by an expression of the Current type.
This set, which is empty at the beginning of the compilation
process will grow, following the smart_eiffel.status evolution.
Thus, if the type of Current is a reference type, the
run_time_set has only reference run classes elements. If the
type of Current is an expanded type, the run_time_set has
only Current as a single element. Futhermore, the size of the
run_time_set depends on live assignments (as well as argument
passing and creation statements) that are found in the live code.