SystemVerilog OOP Mastery · All levels
Callbacks and Policy Classes for Open Extension: Concept Explained
Concept Explained for Callbacks and Policy Classes for Open Extension.
Concept
In short: Callbacks let you inject behavior at lifecycle hooks, while policy classes encapsulate algorithm choices; together they reduce inheritance forks and keep extension points explicit.
Callbacks are event interception points. In UVM, they are powerful for pre/post behavior around a fixed owner component (driver, monitor, sequence) without cloning that component.\n\nPolicy classes are Strategy objects passed into a component so behavior is selected by composition. They are better when you need deterministic, inspectable algorithm switching (for example comparison rules or retry strategy).\n\nA practical rule: callbacks for cross-cutting hooks around existing control flow, policies for core decision logic that you want unit-testable and replaceable at integration time.