Because the implementation-file emitters never change any existing code within a previously generated implementation file, changing the parents of a class requires extremely careful attention by the programmer. For example, for overridden methods, changing a class's parents may invalidate previous parent-method calls provided by the template, and require the addition of new parent-method calls. Neither of these issues is addressed by the incremental update of previously generated method-procedure templates.

The greatest danger from changing the parents of a class, however, concerns the ancestor-initializer calls provided in the stub procedures for initializer methods. (For further information on ancestor initializer calls, see "Initializing and Uninitializing Objects" later in this chapter.) Unlike parent-method calls, ancestor-initializer calls are not optional - they must be made t all classes specified in a directinitclasses modifier, and these calls should always include the parents of the class (the default when no directinitclasses modifier is given). When the parents of a class are changed, however, the ancestor-initializer calls (which must be made in a specific order) are not updated.

The easiest way to deal with this problem is to change the method name of the previously generated initializer stub procedure in the implementation template file. Then, the SOM Compiler can correctly generate a completely new initializer stub procedure (while ignoring the renamed procedure). Once this is done, your customization code from the renamed initializer procedure can be "merged" into the newly generated one, after which the renamed initializer procedure can be deleted.