Var : access T := ... Var_To_Cst : access constant T := ... Cst : constant access T := ... Cst_To_Cst : constant access constant T := ...
In this section, we will refer to a stand-alone object of an anonymous access type as an SO.
When the restriction is in effect, the “statically deeper” relationship
(see RM 3.10.2(4)) does apply to the type of a SO (contrary to RM 3.10.2(19.2))
and, for the purposes of compile-time checks, the accessibility level of the
type of a SO is the accessibility level of that SO.
This supports many common use-cases without the employment of Unchecked_Access
while still removing the need for dynamic checks.
This statically disallows cases that would otherwise require a dynamic accessibility check, such as
type Ref is access all Integer;
Ptr : Ref;
Good : aliased Integer;
procedure Proc is
Bad : aliased Integer;
Stand_Alone : access Integer;
begin
if <some condition> then
Stand_Alone := Good'Access;
else
Stand_Alone := Bad'Access;
end if;
Ptr := Ref (Stand_Alone);
end Proc;
If a No_Dynamic_Accessibility_Checks restriction is in effect, then the otherwise-legal type conversion (the right-hand side of the assignment to Ptr) becomes a violation of the RM 4.6 rule “The accessibility level of the operand type shall not be statically deeper than that of the target type …”.