Ada Reference Manual — Legal Information

12.5.4 Formal Access Types

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The category determined for a formal access type is the category of all access types.

Syntax

formal_access_type_definition ::= access_type_definition

Legality Rules

For a formal access-to-object type, the designated subtypes of the formal and actual types shall statically match.

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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). If and only if the formal subtype excludes null, the actual subtype shall exclude null.

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.

Examples

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);