3.4. Modifying Arguments

The conversion-rule node allows you to write customized code to convert the given argument between the target language and C++, and it is a child of the modify-argument node.

<modify-argument ...>
<conversion-rule class="target | native">
    // the code
</conversion-rule>
</modify-argument>

This node is typically used in combination with the replace-type and remove-argument nodes. The given code is used instead of the generator’s conversion code.

Writing %N in the code (where N is a number), will insert the name of the nth argument. Alternatively, %in and %out which will be replaced with the name of the conversion’s input and output variable, respectively. Note the output variable must be declared explicitly, for example:

<conversion-rule class="native">
bool %out = (bool) %in;
</conversion-rule>

The remove-argument node removes the given argument from the function’s signature, and it is a child of the modify-argument node.

<modify-argument>
    <remove-argument />
</modify-argument>

The remove-default-expression node disables the use of the default expression for the given argument, and it is a child of the modify-argument node.

<modify-argument...>
    <remove-default-expression />
</modify-argument>

The replace-default-expression node replaces the specified argument with the expression specified by the with attribute, and it is a child of the modify-argument node.

<modify-argument>
    <replace-default-expression with="..." />
</modify-argument>

The replace-type node replaces the type of the given argument to the one specified by the modified-type attribute, and it is a child of the modify-argument node.

<modify-argument>
    <replace-type modified-type="..." />
</modify-argument>

If the new type is a class, the modified-type attribute must be set to the fully qualified name (including name of the package as well as the class name).

The define-ownership tag indicates that the function changes the ownership rules of the argument object. The class attribute specifies the class of function where to inject the ownership altering code. The owner attribute specifies the new ownership of the object. It accepts the following values:

• target: the target language will assume full ownership of the object.

  The native resources will be deleted when the target language object is finalized.

• c++: The native code assumes full ownership of the object. The target

  language object will not be garbage collected.

• default: The object will get default ownership, depending on how it

  was created.

<modify-argument>
      <define-ownership class="target | shell"
                        owner="target | c++ | default" />
 </modify-argument>

The replace-value attribute lets you replace the return statement of a function with a fixed string. This attribute can only be used for the argument at index 0, which is always the function’s return value.

<modify-argument index="0" replace-value="this"/>

The parent node lets you define the argument parent which will take ownership of argument and will destroy the C++ child object when the parent is destroyed.

<modify-argument index="1">
      <parent index="this" action="add | remove" />
</modify-argument>

In the index argument you must specify the parent argument. The action add creates a parent link between objects, while remove will undo the parentage relationship.