[RM D.7] This restriction ensures at compile time that barriers in entry declarations for protected types are restricted to either static boolean expressions or references to simple boolean variables defined in the private part of the protected type. No other form of entry barriers is permitted.
The restriction Boolean_Entry_Barriers is recognized as a
synonym for Simple_Barriers. This is retained for historical
compatibility purposes (and a warning will be generated for its use if
warnings on obsolescent features are activated).