Before type-casting an e variable ("as_a"), we often want to check the validity of the operation (this is quite similar in concept to $cast in SystenVerilog). The reason is simple, in case the casting operation failed we would end up with a fatal error at run-time that otherwise could have been avoided. But how?

Here's one elegant way to do it:

type ttt: [E1=3, E2=10];
extend sys {
 run() is also {
 var x: byte = 3; // try x=7 too
  if x.as_a(ttt) in all_values(ttt) then { out( *** X IS IN RANGE *** ) };
 };
 };

In this small example we were trying to convert (type-cast) x from byte to ttt. The method all_values() returns a list of all possible scalar types (in our case - for type ttt). Try this code with x=3 and with x=7 and see what happens.