[Oberon] Protocols (interfaces) in Oberon-2

[Andreas Pirklbauer]

    > Andreas, in your scheme can you create separate protocols, for example
    > "Jsonify" with the method ToJSON and a different protocol "Persistify" with
    > the methods "Store" and "Load", and have other records implement one or the
    > other or neither or both?

Here is what - I think? - you mean (no multiple inheritance in this example):


  MODULE JSONProtocol;  (*protocol definition*)
    TYPE JSON* = POINTER TO JSONDesc;
      JSONDesc* = RECORD data*: ... END ;
    PROCEDURE^ (j: Text) ToJSON* (...);
  END JSONProtocol;

  MODULE PersistProtocol;  (*protocol definition*)
    TYPE Persist* = POINTER TO PersistDesc;
      PersistDesc* = RECORD data*: ... END ;
    PROCEDURE^ (p: Persist) Store* (…);
    PROCEDURE^ (p: Persist) Load* (...);
  END PersistProtocol;

  MODULE Client;
    IMPORT JSONProtocol, PersistProtocol;

    TYPE
      JSON* = POINTER TO JSONDesc;
      JSONDesc* = RECORD (JSONProtocol.JSONDesc) … END ;  (*implements JSONProtocol.JSONDesc*)
    
      Persist* = POINTER TO PersistDesc;
      PersistDesc* = RECORD (PersistProtocol.PersistDesc)… END ;  (*implements PersistProtocol.PersistDesc*)

    PROCEDURE (j: Text) ToJSON* (...);
    BEGIN (*implementation of ToJSON*)
    END ToJSON;

    PROCEDURE (p: Persist) Store* (…);
    BEGIN (*implementation of Store*)
    END Store;

    PROCEDURE (p: Persist) Load* (…);
    BEGIN (*implementation of Load*)
    END Load;

  END Client;