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1-146 SOMobjects Base Toolkit: Programmer’s Reference Manual

somInit Method

Purpose

Initializes instance variables or attributes in a newly created object. Designed to be

overridden.

Note: The newer somDefaultInit method is suggested instead.

IDL Syntax

void somInit ( );

Note: For backward compatibility, this method does not take an Environment parameter.

Description

The somInit method is invoked to cause a newly created object to initialize its instance

variables or attributes.

Note: The newer somDefaultInit method performs object initialization more efficiently and

is now the preferred approach for overriding initialization in an implementation file.

(The somInit method still executes correctly as before.)

Because instances of SOMObject do not have any instance data, the default

implementation does nothing. It is provided as a convenience to class implementors so that

initialization of objects can be done in a uniform way across all classes (by overriding

somInit). This method is called automatically by somNew during object creation.

A companion method, somUninit, is called whenever an object is freed. These two

methods should be designed to work together, with somInit priming an object for its first

use, and somUninit preparing the object for subsequent release.

If objects of your class contain instance variables or attributes, override the somInit method

to initialize the instance variables or attributes when instances of the class are created.

When overriding this method, always call all parent (base) classes’ versions of this method

before doing your own initialization, as follows:

1. The overriding implementation should invoke the parent method for each parent. For

users of the C or C++ implementation bindings, this can be done in either of two ways:

a. By calling a <className>_parents_<methodName> macro (which automatically

invokes all parent methods) or

b. By calling the <className>_parent_<parentName>_<methodName> macro on each

parent separately.

For more information on parent method calls, see the topic “Extending the

Implementation Template” in Chapter 5, “Implementing Classes in SOM,” of the SOM

Toolkit User’s Guide.

2. The code must be written so that it can be executed multiple times without harm on the

same object. This is necessary because, under multiple inheritance, parent method calls

that progress up the inheritance hierarchy may encounter the same ancestor class more

than once (where different inheritance paths “join” when followed backward). A check

can be made to determine whether a particular invocation of somInit is the first on a

given object by examining the contents of its instance variables; all the instance

variables of a newly created SOM object are set to zero before somInit is invoked on

that object.

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