7.10 Built-in Methods

SystemVerilog introduces classes and the method calling syntax, in which a task or function is called using the (.) dot notation:

object.task_or_function()

The object uniquely identifies the data on which the task or function operates. Hence, the method concept is naturally extended to built-in types in order to add functionality that traditionally was done via system tasks or functions. Unlike system tasks, built-in methods are not prefixed with a $ since they require no special prefix to avoid collisions with user-defined identifiers. Thus, the method syntax allows extending the language without the addition of new keywords or cluttering the global name space with system tasks.

Built-in methods, unlike system tasks, can not be redefined by users via PLI tasks. Thus, only functions that users should not be allowed to redefine are good candidates for method calls.

In general, a method is preferred over a system task when a particular functionality applies to all data types, or it applies to a specific data. For example:

dynamic_array.size, associative_array.num, and string.len

These are all similar concepts, but they represent different things. A dynamic array has a size, an associative array contains a given number of items, and a string has a given length. Using the same system task, such as $length, for all of them would be less clear and intuitive.

A method can only be associated with a particular data type, therefore, if some functionality is a simple side effect (i.e., $stop or $reset) or it operates on no specific data (i.e., $random) then a system task must be used.