Add a variable to a class instance at runtime: Difference between revisions

Unicon implements object environments with records and supporting procedures for creation, initialization, and methods. To modify an instance you must create a new record then copy, amend, and amendreplace it. Strictly speaking we can't guarantee the replace as there is no way to modify the existing object and we are creating a new instance with extensions. The procedures ''constructor'' and ''fieldnames'' are needed. This example doesn't do error checking. Here ''extend'' takes three arguments, the class instance, a list of new variable names as strings, and an optional list of new values to be assigned. The new instance is returned and the object is replaced by assignment. The caveat here is that if the object was assigned to anything else we will now have two objects floating around with possible side effects. As written this isn't safe from name collisions - aside from local declarations the use of a fixed constructor name uses the global name space. There is a final caveat that needs to be observed - if future implementations of objects change then this could easily stop working.