ABSTRACT operator

The ABSTRACT operator creates an abstract action.

Syntax

ABSTRACT [type [exclusionType] [order]] [FULL] [(argClassName1, ..., argClassNameN)] [returnClassName [(returnArgClassName1, ..., returnArgClassNameM)]]

Description

The ABSTRACT operator creates an abstract action. Its implementations are added later by ACTION+ statements. Depending on the selected type, the platform builds from them the behavior of a branch operator or a sequence operator.

The ABSTRACT operator is a context-independent action operator, so it can only be used in the ACTION statement.

Parameters

• type

  Option. Possible values:

  • CASE - the explicit conditional form of the abstract action. The selection condition of each implementation is defined in the corresponding ACTION+ statement using the WHEN block.
  • MULTI - a polymorphic form of the abstract action. An implementation is selected when the current arguments are compatible with its signature.
  • LIST - the sequential form of the abstract action. In this form all implementations are executed one after another.

  If this option is omitted, MULTI is used by default.

• exclusionType

  Option. It specifies the type of mutual exclusion. Possible values:

  • EXCLUSIVE - the mutually exclusive mode for the CASE and MULTI forms. In this mode, for each set of arguments there must be at most one matching implementation.
  • OVERRIDE - the mode for the CASE and MULTI forms in which several implementations may match simultaneously.

  Used only with CASE or MULTI. For CASE, OVERRIDE is used by default; for MULTI, EXCLUSIVE is used by default.

• order

  Option. Possible values:

  • FIRST - for the CASE and MULTI forms with OVERRIDE, new implementations are added to the beginning of the list, so the last added matching implementation is executed. For the LIST form, it sets the execution order reverse to the addition order. If this value is not specified after OVERRIDE, it is used by default.
  • LAST - for the CASE and MULTI forms with OVERRIDE, new implementations are added to the end of the list, so the first added matching implementation is executed. For the LIST form, it sets the execution order equal to the addition order and is used by default.

  Used either after OVERRIDE for the CASE and MULTI forms or after LIST.

• FULL

  Keyword. If specified, the platform automatically checks the completeness of implementations: for all descendants of the argument classes there must be at least one applicable implementation, or exactly one if the conditions are mutually exclusive.

• argClassName1, ..., argClassNameN

  List of class names of action arguments. Each name is defined by a class ID. The list may be empty. If the list is omitted, the parameter classes are taken from the ACTION statement in which the ABSTRACT operator is used.

• returnClassName

  Name of the class of the value returned by the action. It is defined by a class ID. If this parameter is specified, the abstract action is declared as an action with a result.

• returnArgClassName1, ..., returnArgClassNameM

  List of class names of the additional parameters on which the returned value depends. It is used when the action returns not a single value, but a set of values over those parameters. Each name is defined by a class ID. The list may be empty.

Examples

exportXls 'Export to Excel' ABSTRACT CASE OVERRIDE LAST (Order);
exportXls (Order o) + WHEN name(currency(o)) == 'USD' THEN {
    MESSAGE 'Export USD not implemented';
}

CLASS ABSTRACT Task;
run 'Execute' ABSTRACT MULTI EXCLUSIVE FULL (Task);

CLASS Task1 : Task;
name = DATA STRING[100] (Task);
run (Task1 t) + {
    MESSAGE 'Run Task1 ' + name(t);
}

onStarted ABSTRACT LIST ();
onStarted () + {
    MESSAGE 'Preparing data';
}
onStarted () + {
    MESSAGE 'Starting handlers';
}

CLASS Issue;
CLASS Language;
localizedTitle = DATA STRING[100] (Issue, Language);

getLocalizedTitle(Issue issue) ABSTRACT STRING[100] (Language);
getLocalizedTitle (Issue issue) + {
    FOR Language l IS Language DO
        RETURN localizedTitle(issue, l);
}