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User objects that behave like structures – PB Docs 126 – PowerBuilder Library

User objects that behave like structures – PB Docs 126

User objects that behave like structures

In PowerBuilder, a nonvisual user object can provide functionality
similar to that of a structure. Its instance variables form a collection
similar to the variables for the structure. In scripts, you use
dot notation to refer to the user object’s instance variables,
just as you do for structure variables.

Advantages of user objects

The user object can include functions and its own structure
definitions, and it allows you to inherit from an ancestor class.
None of this is possible with a structure definition.

Memory allocation differences

Memory allocation is different for user objects and structures.
An object variable is a reference to the object. Declaring the variable
does not allocate memory for the object. After you declare it, you
must instantiate it with a CREATE statement.
Assignment for a user object is also different (described in “Assignment for objects and
structures “
).

Autoinstantiated objects

If you want a user object that has methods and inheritance
but want the memory allocation of a structure, you can define an
autoinstantiated object.

You do not have to create and destroy autoinstantiated objects.
Like structures, they are created when they are declared and destroyed
when they go out of scope. However, because assignment for autoinstantiated
objects behaves like structures, the copies made of the object can
be a drawback.

To make a custom class user object autoinstantiated, select
the Autoinstantiate check box on the user object’s property
sheet.


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