Design Patterns, The Decorator

Question

When trying to implement the classic decorator design patterns your decorator executable might look like this:<br><br>
<pre>
  METHOD validate.
    DATA: Validator TYPE REF TO validation_manager.
   CREATE OBJECT:
     Validator TYPE validation_manager.
    ,Validator TYPE validate_format                 EXPORTING x_validator = Validator
    ,Validator TYPE validate_values                 EXPORTING x_validator = Validator
    ,Validator TYPE validate_relation_input       EXPORTING x_validator = Validator
    ,Validator TYPE validate_relation_database EXPORTING x_validator = Validator.
    me->lst_result = validator->validate( me->lst_data ).
    WRITE: / 'Processing Validate Activity'.
  ENDMETHOD.                    "validate</pre><br><br>
The validate method ends up in endless resurcion in the memory. The reason is that I'm using the same variable as the resulting instanse and as parameter. It seems like the constructor treats both the result and the parameter as the same field/instanse regardless import parameter such as VALUE/REFERENCE. If I change the method to use an extra field in the method validate like:
<br><br><pre>
  METHOD validate.
    DATA:
      validator  TYPE REF TO validation_manager
     ,recursive  TYPE REF TO validation_manager.
    CREATE OBJECT validator TYPE validation_manager.
    recursive ?= validator.
    CREATE OBJECT validator TYPE validate_format
      EXPORTING x_validator = recursive.
    recursive ?= validator.
    CREATE OBJECT validator TYPE validate_values
     EXPORTING x_validator = recursive.
    recursive ?= validator.
    CREATE OBJECT validator TYPE validate_relation_input
      EXPORTING x_validator = recursive.
    recursive ?= validator.
    CREATE OBJECT validator TYPE validate_relation_database
      EXPORTING x_validator = recursive .
    recursive ?= validator.
    me->lst_result = validator->validate( me->lst_data ).
    WRITE: / 'Processing Validate Activity'.
  ENDMETHOD.                    "validate</pre><br><br>
Now the decorator engine works, but why does the first implementation not work when the same one executes fine in php, c++, delphi, java and other languages.<br><br>
If you do not know what I'm trying to discuss, look up "Design Patterns - Simply", and jump to the chapter about the decorator design pattern. I'm trying to use this design pattern for a validation manager within my Business Process Engine, which needs to be able to configure what types of validation needed for on specific process (BPMN).<br><br>

Answer 1

Hi Matt, Thanks for the formatting..:) I will post the complete program as it's only a prototype program. Trying to get the format under control.
</body>
Report  ZDP_DECORATOR_XMP01
REPORT  zdp_decorator_xmp01.
parameters: bestimpl  TYPE boolean_01 default 0.
TYPES:
  BEGIN OF processdata
   ,name   TYPE char30
   ,street TYPE char30
   ,zip    TYPE char5
   ,city   TYPE char30
   ,email  TYPE char50
   ,phone  TYPE char20
,END OF processdata
,BEGIN OF result
   ,msgid  TYPE msgid
   ,msgtyp TYPE msgty
   ,msgno  TYPE msgno
   ,status TYPE char1
,END OF result.
CONSTANTS:
true     TYPE boolean_01 VALUE 1
,false    TYPE boolean_01 VALUE 0.
CLASS validationmanager DEFINITION
CLASS validation_manager DEFINITION.
  PUBLIC SECTION.
    METHODS:
      validate
        IMPORTING
          x_data             TYPE processdata
        RETURNING
          value(y_result)    TYPE result.
ENDCLASS.
CLASS validationmanager IMPLEMENTATION
CLASS validation_manager IMPLEMENTATION.
  METHOD validate.
    WRITE: / 'Common validation'.
  ENDMETHOD.                    "validate
ENDCLASS.
CLASS Validate_Decorator DEFINITION
CLASS validate_decorator DEFINITION INHERITING FROM validation_manager ABSTRACT .
  PUBLIC SECTION.
    DATA: validator TYPE REF TO validation_manager.
ENDCLASS. 
CLASS validate_format DEFINITION
CLASS validate_format DEFINITION INHERITING FROM validate_decorator.
  PUBLIC SECTION.
    METHODS:
      constructor
       IMPORTING value(x_validator) TYPE REF TO validation_manager
     ,validate REDEFINITION.
ENDCLASS.   
CLASS validate_format IMPLEMENTATION
CLASS validate_format IMPLEMENTATION.
  METHOD constructor.
    CALL METHOD super->constructor( ).
    me->validator = x_validator.
  ENDMETHOD.                    "constructor
  METHOD validate.
    y_result = validator->validate( x_data ).
    IF y_result-status IS INITIAL.
      WRITE: / 'Now doing the format checks'.
    ENDIF.
  ENDMETHOD.                    "validate
ENDCLASS.
CLASS validate_values DEFINITION
CLASS validate_values  DEFINITION INHERITING FROM validate_decorator.
  PUBLIC SECTION.
    METHODS:
      constructor
       IMPORTING value(x_validator) TYPE REF TO validation_manager
     ,validate REDEFINITION.
ENDCLASS.
CLASS validate_values IMPLEMENTATION
CLASS validate_values IMPLEMENTATION.
  METHOD constructor.
    CALL METHOD super->constructor( ).
    me->validator = x_validator.
  ENDMETHOD.                    "constructor
  METHOD validate.
    y_result = validator->validate( x_data ).
    IF y_result-status IS INITIAL.
      WRITE: / 'Now doing the values checks'.
    ENDIF.
  ENDMETHOD.                    "validate
ENDCLASS. 
CLASS validate_relation_input DEFINITION
CLASS validate_relation_input DEFINITION INHERITING FROM validate_decorator.
  PUBLIC SECTION.
    METHODS:
      constructor
       IMPORTING value(x_validator) TYPE REF TO validation_manager
     ,validate REDEFINITION.
ENDCLASS.
CLASS validate_relation_input IMPLEMENTATION
CLASS validate_relation_input IMPLEMENTATION.
  METHOD constructor.
    CALL METHOD super->constructor( ).
    me->validator = x_validator.
  ENDMETHOD.                    "constructor
  METHOD validate.
    y_result = validator->validate( x_data ).
    IF y_result-status IS INITIAL.
      WRITE: / 'Now doing the relation input checks'.
    ENDIF.
  ENDMETHOD.                    "validate
ENDCLASS.
CLASS validate_relation_database DEFINITION
CLASS validate_relation_database DEFINITION INHERITING FROM validate_decorator.
  PUBLIC SECTION.
    METHODS:
      constructor
       IMPORTING value(x_validator) TYPE REF TO validation_manager
     ,validate REDEFINITION.
ENDCLASS.  
CLASS validate_relation_database IMPLEMENTATION
CLASS validate_relation_database IMPLEMENTATION.
  METHOD constructor.
    CALL METHOD super->constructor( ).
    me->validator = x_validator.
  ENDMETHOD.                    "constructor
  METHOD validate.
    y_result = validator->validate( x_data ).
    IF y_result-status IS INITIAL.
      WRITE: / 'Now doing the relation database checks'.
    ENDIF.
  ENDMETHOD.                    "validate
ENDCLASS.  
CLASS process_execution DEFINITION
CLASS process_execution DEFINITION.
  PUBLIC SECTION.
    METHODS:
      startevent
     ,getdata
     ,validate
     ,process
     ,endevent.
  PRIVATE SECTION.
    DATA:
      lst_data   TYPE processdata
     ,lst_result TYPE result.
ENDCLASS.                    "process_execution DEFINITION
CLASS process_execution IMPLEMENTATION
CLASS process_execution IMPLEMENTATION.
  METHOD startevent.
    WRITE: / 'Processing startevent'.
  ENDMETHOD.                    "startevent
  METHOD getdata.
    me->lst_data-name        = 'Hans Andersen'.
    me->lst_data-street      = 'H.C Andersens Boulevard 112'.
    me->lst_data-zip         = '1557'.
    me->lst_data-city        = 'København'.
    me->lst_data-email       = 'hcATandersen.dk'.
    me->lst_data-phone       = '0045-31162211'.
    WRITE: / 'Processing Get_Data Activity'.
  ENDMETHOD.                    "getdata
  METHOD validate.
    DATA:
      validator  TYPE REF TO validation_manager
     ,recursive  TYPE REF TO validation_manager
    IF bestimpl = true.
      CREATE OBJECT:
        validator TYPE validation_manager
       ,validator TYPE validate_format EXPORTING x_validator = recursive
       ,validator TYPE validate_values EXPORTING x_validator = recursive
       ,validator TYPE validate_relation_input EXPORTING x_validator = recursive
       ,validator TYPE validate_relation_database EXPORTING x_validator = recursive.
    ELSE.
      CREATE OBJECT validator TYPE validation_manager.
      recursive ?= validator.
      CREATE OBJECT validator TYPE validate_format
        EXPORTING x_validator = recursive.
      recursive ?= validator.
      CREATE OBJECT validator TYPE validate_values
       EXPORTING x_validator = recursive.
      recursive ?= validator.
      CREATE OBJECT validator TYPE validate_relation_input
        EXPORTING x_validator = recursive.
      recursive ?= validator.
      CREATE OBJECT validator TYPE validate_relation_database
        EXPORTING x_validator = recursive .
      recursive ?= validator.
    ENDIF.
  Recursive call of the validate and it's successors
    me->lst_result = validator->validate( me->lst_data ).
    WRITE: / 'Processing Validate Activity'.
  ENDMETHOD.                    "validate
  METHOD process.
    WRITE: / 'Processing Process Activity'.
  ENDMETHOD.                    "process
  METHOD endevent.
    WRITE: / 'Processing endevent'.
  ENDMETHOD.                    "endevent
ENDCLASS.    
CLASS mainapp DEFINITION                                             *
CLASS mainapp DEFINITION.
  PUBLIC SECTION.
    CLASS-METHODS:
      main.
ENDCLASS.   
CLASS mainapp IMPLEMENTATION                                         *
CLASS mainapp IMPLEMENTATION.
  METHOD main.
    DATA:
      p89 TYPE REF TO process_execution.
    CREATE OBJECT p89.
    p89->startevent( ).
    p89->getdata( ).
    p89->validate( ).
    p89->process( ).
    p89->endevent( ).
  ENDMETHOD.  
ENDCLASS.     
START-OF-SELECTION.
  mainapp=>main( ).
Edited by: Matt on Dec 22, 2009 2:03 PM Fixed formatting