[GNAT] No dynamic accessibility checks are generated when this restriction is in effect. Instead, dangling references are prevented via more conservative compile-time checking. More specifically, existing compile-time checks are enforced but with more conservative assumptions about the accessibility levels of the relevant entities. These conservative assumptions eliminate the need for dynamic accessibility checks.
These new rules for computing (at compile-time) the accessibility level of an anonymous access type T are as follows:
For any other accessibility level L such that the level of parameters and local variables of the callee is statically deeper than L, the level of T (from the callee’s perspective) is also statically deeper than L.