12.5.4 Formal Access Types
The class determined for a formal access type is the class of all access types.
formal_access_type_definition ::= access_type_definition
For a formal access-to-object type, the designated subtypes of the formal and actual types shall statically match.
If and only if the general_access_modifier constant applies to the formal, the actual shall be an access-to-constant type. If the general_access_modifier all applies to the formal, then the actual shall be a general access-to-variable type (see 3.10).
For a formal access-to-subprogram subtype, the designated profiles of the formal and the actual shall be mode-conformant, and the calling convention of the actual shall be protected if and only if that of the formal is protected.
Example of formal access types:
-- the formal types of the generic package
generic type Node is private; type Link is access Node; package P is ... end P;
-- can be matched by the actual types
type Car; type Car_Name is access Car;
type Car is record Pred, Succ : Car_Name; Number : License_Number; Owner : Person; end record;
-- in the following generic instantiation
package R is new P(Node => Car, Link => Car_Name);
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Copyright © 2000 The MITRE Corporation, Inc. Ada Reference Manual