Pragma Implemented

Syntax:

     pragma Implemented (procedure_LOCAL_NAME, implementation_kind);
     
     implementation_kind ::= By_Entry | By_Protected_Procedure | By_Any

This is an Ada 2012 representation pragma which applies to protected, task and synchronized interface primitives. The use of pragma Implemented provides a way to impose a static requirement on the overriding operation by adhering to one of the three implementation kinds: entry, protected procedure or any of the above. This pragma is available in all earlier versions of Ada as an implementation-defined pragma.

     type Synch_Iface is synchronized interface;
     procedure Prim_Op (Obj : in out Iface) is abstract;
     pragma Implemented (Prim_Op, By_Protected_Procedure);
     
     protected type Prot_1 is new Synch_Iface with
        procedure Prim_Op;  --  Legal
     end Prot_1;
     
     protected type Prot_2 is new Synch_Iface with
        entry Prim_Op;      --  Illegal
     end Prot_2;
     
     task type Task_Typ is new Synch_Iface with
        entry Prim_Op;      --  Illegal
     end Task_Typ;

When applied to the procedure_or_entry_NAME of a requeue statement, pragma Implemented determines the runtime behavior of the requeue. Implementation kind By_Entry guarantees that the action of requeueing will proceed from an entry to another entry. Implementation kind By_Protected_Procedure transforms the requeue into a dispatching call, thus eliminating the chance of blocking. Kind By_Any shares the behavior of By_Entry and By_Protected_Procedure depending on the target's overriding subprogram kind.