ITT Rule IDL Version 7.0 User Manual download pdf (Page 167)

Chapter 7: Creating an Operation 167

iTool Developer’s Guide Creating a New Generalized Operation

struct = { ExampleOp, INHERITS IDLitOperation}

END

Discussion

The purpose of the structure definition routine is to define a named IDL structure

with structure fields that will contain the operation object instance data. The structure

name should be the same as the operation’s class name — in this case,

ExampleOp.

Like many iTool operations that act on data,

ExampleOp is created as a subclass of

the IDLitOperation class. The ExampleOp Operation class does not include any

instance data of its own.

Note

This example is intended to demonstrate how simple it can be to create a new

operation class definition. While the class definition for an operation class with

significant extra functionality will likely define additional structure fields, and may

inherit from other iTool classes, the basic principles are the same.

Creating an Init Method

The operation class Init method handles any initialization required by the operation

object, and should do the following:

• define the Init function method, using the keyword inheritance mechanism to

handle “extra” keywords

• call the Init methods of any superclasses, using the keyword inheritance

mechanism to pass “extra” keywords

• register any properties of the operation, and set property attributes as necessary

• perform other initialization steps as necessary

• return the value 1 if the initialization steps are successful, or 0 otherwise

Definition of the Init Function

Begin by defining the argument and keyword list for your Init method. The argument

and keyword list defines positional parameters (arguments) accepted by your method,

defines any keywords that will be handled directly by your method, and specifies

whether keywords not explicitly handled by your method will be passed through to

other routines called by your method via IDL’s keyword inheritance mechanism.

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ITT Rule IDL Version 7.0 User Manual Page 167