# Policy Classes

Each of UVM’s policy classes perform a specific task for uvm_object-based objects: printing, comparing, recording, packing, and unpacking. They are implemented separately from uvm_object so that users can plug in different ways to print, compare, etc. without modifying the object class being operated on. The user can simply apply a different printer or compare “policy” to change how an object is printed or compared.

Each policy class includes several user-configurable parameters that control the operation. Users may also customize operations by deriving new policy subtypes from these base types. For example, the UVM provides four different uvm_printer-based policy classes, each of which print objects in a different format.

- uvm_printer - performs deep printing of uvm_object-based objects. The UVM provides several subtypes to uvm_printer that print objects in a specific format: uvm_table_printer, uvm_tree_printer, and uvm_line_printer. Each such printer has many configuration options that goven what and how object members are printed.
- uvm_comparer - performs deep comparison of uvm_object-based objects. Users may configure what is compared and how miscompares are reported.
- uvm_recorder - performs the task of recording uvm_object-based objects to a transaction data base. The implementation is vendor-specific.
- uvm_packer - used to pack (serialize) and unpack uvm_object-based properties into bit, byte, or int arrays and back again.

Summary

Policy Classes
Each of UVM’s policy classes perform a specific task for uvm_object-based objects: printing, comparing, recording, packing, and unpacking.

> virtual class uvm_object extends uvm_void

The uvm_object class is the base class for all UVM data and hierarchical classes.

> virtual class uvm_printer

The uvm_printer class provides an interface for printing uvm_objects in various formats.

> class uvm_table_printer extends uvm_printer

The table printer prints output in a tabular format.

> class uvm_tree_printer extends uvm_printer

By overriding various methods of the uvm_printer super class, the tree printer prints output in a tree format.

> class uvm_line_printer extends uvm_tree_printer

The line printer prints output in a line format.

> class uvm_comparer

The uvm_comparer class provides a policy object for doing comparisons.

> virtual class uvm_recorder extends uvm_object

Abstract class which defines the recorder API.
The uvm_packer class provides a policy object for packing and unpacking uvm_objects.