About the API History

This chapter collects information about changes to IDL's Application Programmer's Interface (API) — the procedures, functions, object classes, object methods, and other features that make up the IDL language. For each IDL release, we list features that were added to IDL and features that were made obsolete.

Note
Information about changes is also included at the end of each routine's reference section, in a section titled Version History.

What Are Obsolete Features?

To improve the overall quality and functionality of IDL, ITT Visual Information Solutions occasionally replaces existing features with new, improved features. In many cases, existing routines are improved without changing their existing behavior—through improvements of the underlying algorithms, for example, or by adding keyword functionality. In some cases, however, the improved methods are incompatible with the old. In these situations, we consider the routines that we have replaced to be obsolete.

For similar reasons, arguments and keywords to existing routines may occasionally become obsolete. In many cases, the functionality activated by the obsolete argument or keyword can be achieved more efficiently using a new argument or keyword. If this is the case, existing code using the obsolete argument or keyword will generally continue to function as it always has, although performance may be better using the new, replacement argument or keyword. In cases where the obsolete argument or keyword activated functionality that is no longer available (perhaps as a result of an operating system upgrade or change), IDL will either quietly ignore the presence of the argument or keyword (if doing so does not affect the resulting output) or warn that an invalid parameter has been specified.

This topic lists the features that have become obsolete in each version of IDL. These features are not documented along with current IDL routines. To view reference information for features obsoleted in IDL version 5.0 and later, see the Obsolete IDL Features guide. Features obsoleted in IDL 4.0 and earlier are not documented in the Obsolete IDL Features guide. If a .pro file for the routine exists, it is located in the lib/obsolete subdirectory of the IDL distribution. You can read the documentation header of a routine in the obsolete directory either by opening the .pro file or using the DOC_LIBRARY routine.