Parse Structured form
Completing the Parameters tab

Use the Parameters tab to identify any variables used as input parameters to, or results from, the parse structured rule.

Understanding parameters

This tab is optional; not every parse structured rule has parameters. When the rule is called, the system places parameter names and values on a nameless, classless page known as the parameter page, and noted by the prefix keyword param. For example, param.depth refers to the depth parameter.

The declared type of a parameter (such as Integer, Double, or DateTime) indicates the format of a value. When evaluating expressions, the Pega Platformfollows the same casting and type conversion operations as for properties.

Parameter names are not properties, and are not defined by a property:

• If the parameter is an input to the rule, you can access the values received from the calling activity, using the Param keyword followed by the parameter name (though the parameters are not truly properties).
• If the parameter is an output (result) of the rule, your activity can set values for it using the Property-Set method with the Param keyword followed by the parameter name. (The parameter page is available to the calling rule only when the Pass current parameter page? check box is selected in the Call instruction.)
• Parameter names must be distinct.
• Validation of the Parse Structured rule form does not require that every parameter referenced on the Steps tab be listed on the Parameters tab. Because the Parameters tab supports prompting when other rules call the activity, do list all input parameters. You can omit output parameters.

Recording an activity's outputs or results on the parameter page is only useful when the parameter page is passed into this activity by reference, using the Pass current parameter page? check box in the Call instruction. When checked, one parameter page is shared between the calling and called activity. Otherwise, parameters on the called activity's parameter page are not available to the calling activity after a return.

Notes on Out parameters

The Call instruction examines the In/Out value of each parameter in the called activity:

• If the parameter is declared as Out and the entire parameter page of the current activity is shared with the calling activity, then the value of the Out parameter in the call may be of the form param.name. If the called activity updates the output parameter, the resulting value is available on the parameter page of the calling activity.
• If a parameter is declared as Out and the value of the parameter in the Call panel is itself a property reference, then traditional call-by-reference semantics applies. That is, if the called activity updates the parameter value, the value of the property itself is updated.

Do not list a local variable as the destination for an Out parameter. Do not pass a parameter reference as the destination for an Out parameter, unless passing the entire parameter page.

In a chain of calling activities (activity Alpha calls Beta which calls Gamma), a property passed by reference from Alpha to Beta can also be passed by reference to Gamma, and changes to the Out parameter made within Gamma can be passed all the way back to Alpha. This corresponds to the behavior of call-by-reference in many programming languages.

Completing the Parameters array

Complete a row of this array to define parameters for this activity. Within the activity, you can reference parameters with the keyword param followed by a period and the parameter name.

Reviewing System Parameters

Several input parameters are automatically available for activities used in flow processing — that is, activities with an Activity Type on the Security tab set to Connect, Utility, Route, Notify and Assign. Your activity cannot alter the value of these system-maintained parameters, but can use them as inputs, using the normal Param.Name notation.

For example, system parameter Param.pyDraftMode is true when the flow is in draft mode.

Click Show System Parameters to review the names and descriptions of these parameters. This button is not visible for other activity types. Click Hide System Parameters to hide this area. See How to create activities for flows for information on these and other system parameters.

Completing the Local Variables array

Use the Local Variables section to create scalar variables. Local variables are stored together as fields in the Java class that is generated to implement the activity. These require less memory and execute faster than regular parameters. They are often used to pass information from step to step.

Local variables do not appear on the parameter page.

A local variable of type StringBuffer may be assembled in multiple steps, as a Property-Set on a StringBuffer appends the value to the StringBuffer.

Use the Local keyword to reference a local variable in a Property-Set method.

To avoid Java null pointer exceptions, the system initializes String local variables to the empty string, and the StringBuffer local variable as:

public StringBuffer aBuffer = new StringBuffer();

Three standard methods manipulate String Buffer local variables. See:

•   StringBuffer-Append method 
•   StringBuffer-Insert method 
•   StringBuffer-Reset method 

About Parse Structured rules

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