ABL allows you to specify a variety of data-type specifier and mode options for passing COM object method parameters and setting COM object properties (see Property and method syntax for COM objects). Data-type specifier options specify a data type mapping between COM data types and ABL data types; mode options specify how a method parameter is passed (whether for input or output). Thus:

  • The data-type specifier options in the table Data-types for COM object methods and properties dictate COM data type conversions for passing method input parameters and setting properties that are different than the defaults. (For more information on COM data-type conversion, see COM Object Data Type Mapping)
  • The type options BY-POINTER and BY-VARIANT-POINTER specify additional information for passing method parameters.
  • The mode options OUTPUT and INPUT-OUTPUT specify how the method parameter is used.

One of the essential criteria that determines when and how you might have to use data-type specifier and mode options is the Type Library provided with a COM object implementation.