ABSTRACT operator

The ABSTRACT operator creates an abstract property.

Syntax

ABSTRACT [type [exclusionType]] [CHECKED] returnClassName(argClassName1, ..., argClassNameN)

Where exclusionType is of two types:

EXCLUSIVE
OVERRIDE [FIRST | LAST]

Description

The ABSTRACT operator creates an abstract property, the implementations of which can be defined later (for example, in other modules dependent on the module containing the ABSTRACT property). Implementations are added to the property using the += statement. When calculating an abstract property, its matching implementation is selected and calculated. The selection of the matching implementation depends on the selection conditions that are defined when adding implementations, and on the ABSTRACT operator type.

• CASE - a general case. The selection condition will be explicitly specified in the implementation using the WHEN block.
• MULTI – a polymorphic form. The selection condition is that the parameters match the implementation signature. This type is the default type and need not to be explicitly specified.
• VALUE - a polymorphic form. The selection condition will be definiteness (a none-NULL value) of the implementation value (essentially, the implementation itself).

The type of mutual exclusion of an operator determines whether several conditions for the implementation of an abstract property can simultaneously be met with a certain set of parameters. The EXCLUSIVE type indicates that implementation conditions cannot be met simultaneously. The OVERRIDE type allows several simultaneously met conditions. In this case, the implementation to be selected is determined by the keywords FIRST and LAST.

The ABSTRACT operator cannot be used inside expressions.

Parameters

• type

  Type of abstract property. It is specified by one of the keywords:

  • CASE
  • MULTI
  • VALUE

  The default value is MULTI.

• exclusionType

  Type of mutual exclusion. One of these keywords: EXCLUSIVE or OVERRIDE. Unless explicitly specified, in a MULTI abstract property the default type of mutual exclusion is EXCLUSIVE, and in all other cases the default mutual exclusion type is OVERRIDE.

  • FIRST | LAST

  Keywords. Determine which of the matching implementations will be selected. When the word FIRST is specified, implementations will be added to the top of the implementations list, so that the last added implementation will be selected. When the word LAST is specified, implementations will be added to the end of the implementations list, so that the implementation added first will be selected. If not specified, the default is FIRST.

• FULL

  Keyword. If specified, the platform will automatically check that at least one implementation is specified for all child objects of the argument classes (or exactly one if the conditions are mutually exclusive).

• returnClassName

  Class of the return value of the property. Class ID.

• argClassName1, ..., argClassNameN

  List of class names of property arguments. Each name is defined by a class ID.

Examples

CLASS Invoice;
CLASS InvoiceDetail;
CLASS Range;

// In this case, ABSTRACT MULTI EXCLUSIVE is created
rateChargeExchange(invoice) = ABSTRACT NUMERIC[14,6] (Invoice);
             
// In this case, ABSTRACT CASE OVERRIDE LAST is created, and if there are
// several suitable implementations, the first of them will be calculated
backgroundSku 'Color' (d) = ABSTRACT CASE FULL COLOR (InvoiceDetail);
 
// The last matching implementation will be calculated here
overVAT = ABSTRACT VALUE OVERRIDE FIRST Range (InvoiceDetail);