5.1.72 Pure_Barriers

[GNAT] This restriction ensures at compile time that protected entry barriers are restricted to:

• * simple variables defined in the private part of the protected type/object,
• * constant declarations,
• * named numbers,
• * enumeration literals,
• * integer literals,
• * real literals,
• * character literals,
• * implicitly defined comparison operators,
• * uses of the Standard."not" operator,
• * short-circuit operator

This restriction is a relaxation of the Simple_Barriers restriction, but still ensures absence of side effects, exceptions, and recursion during the evaluation of the barriers.