TAbstractFile = CLASS ABSTRACT
    (***) PROTECTED (***)
      CONST
        MIN_BUF_SIZE  = 64 * 1024;
        MAX_BUF_SIZE  = 1024 * 1024;

      VAR
        fMode:          TDeviceMode;
        fHasKnownSize:  BOOLEAN;
        fSizeIsConst:   BOOLEAN;
        fSize:          INTEGER;
        fPos:           INTEGER;
        fEOF:           BOOLEAN;

    (***) PUBLIC (***)
      (* Core *)

      // Reads 1..Count bytes
      FUNCTION  ReadUpTo
      (
                Count:      INTEGER;
            {n} Buf:        POINTER;
        OUT     BytesRead:  INTEGER
      ): BOOLEAN; VIRTUAL; ABSTRACT;

      // Writes 1..Count bytes
      FUNCTION  WriteUpTo
      (
                Count:        INTEGER;
            {n} Buf:          POINTER;
        OUT     ByteWritten:  INTEGER
      ): BOOLEAN; VIRTUAL; ABSTRACT;

      FUNCTION  Seek (NewPos: INTEGER): BOOLEAN; VIRTUAL; ABSTRACT;

      (* Reading *)
      FUNCTION  Read (Count: INTEGER; {n} Buf: POINTER): BOOLEAN;
      FUNCTION  ReadByte (OUT Res: BYTE): BOOLEAN;
      FUNCTION  ReadInt (OUT Res: INTEGER): BOOLEAN;
      FUNCTION  ReadStr (Count: INTEGER; OUT Res: STRING): BOOLEAN;
      FUNCTION  ReadAllToBuf (OUT Buf: POINTER; OUT Size: INTEGER): BOOLEAN;
      FUNCTION  ReadAllToStr (OUT Str: STRING): BOOLEAN;

      (* Writing *)
      FUNCTION  Write (Count: INTEGER; {n} Buf: POINTER): BOOLEAN;
      FUNCTION  WriteByte (Data: BYTE): BOOLEAN;
      FUNCTION  WriteWord (Data: WORD): BOOLEAN;
      FUNCTION  WriteInt (Data: INTEGER): BOOLEAN;
      FUNCTION  WriteStr (Data: STRING): BOOLEAN;
      FUNCTION  WriteFrom (Count: INTEGER; Source: TAbstractFile): BOOLEAN;
      FUNCTION  WriteAllFrom (Source: TAbstractFile): BOOLEAN;

      PROPERTY  Mode:         TDeviceMode READ fMode;
      PROPERTY  HasKnownSize: BOOLEAN READ fHasKnownSize;
      PROPERTY  SizeIsConst:  BOOLEAN READ fSizeIsConst;
      PROPERTY  Size:         INTEGER READ fSize;
      PROPERTY  Pos:          INTEGER READ fPos;
      PROPERTY  EOF:          BOOLEAN READ fEOF;
  END; // .CLASS TAbstractFile