Importance of functions and events

Much of the power of the PowerScript language resides in the
built-in PowerScript functions that you can use in expressions and
assignment statements.

Types of functions and events

PowerBuilder objects have built-in events and functions. You
can enhance objects with your own user-defined functions and events,
and you can declare local external functions for an object. The
PowerScript language also has system functions that are not associated
with any object. You can define your own global functions and declare
external functions and remote procedure calls.

The following table shows the different types of functions
and events.

Comparing functions and events

Functions and events have the following similarities:

• Both
  functions and events have arguments and return values.

• You can call object functions and events dynamically
  or statically. Global or system functions cannot be called dynamically.

• You can post or trigger a function or event call.

Functions and events have the following differences:

• Functions can be global or part of an object’s
  definition. Events are associated only with objects.

• PowerBuilder uses different search orders when looking
  for events and functions.

• A call to an undefined function triggers an error.
  A call to an undefined event does not trigger an error.

• Object-level functions can be overloaded. Events
  (and global functions) cannot be overloaded.

• When you define a function, you can restrict access
  to it. You cannot add scope restrictions when you define events.

• When functions are inherited, you can extend the
  ancestor function by calling it in the descendant’s script.
  You can also override the function definition. When events are inherited,
  the scripts for those events are extended by default. You can choose
  to extend or override the script.

Which to use

Whether you write most of your code in user-defined functions
or in event scripts is one of the design decisions you must make.
Because there is no performance difference, the decision is based
on how you prefer to interact with PowerBuilder: whether you prefer
the interface for defining user events or that for defining functions,
how you want to handle errors, and whether your design includes
overloading.

It is unlikely that you will use either events or functions
exclusively, but for ease of maintenance, you might want to choose
one approach for handling most situations.