SystemVerilog learning-07-class inheritance and package use

Class inheritance

What is inheritance ?

Inheritance is a key concept of the object-oriented programming paradigm . Class is used to create user-defined types . Inheritance makes it very safe for users to use , Add or modify the behavior of the class in a non intrusive way . The process of extending a base class and generating new subclasses is called class derivation , When a class is extended and created , The derived class inherits the data members of its base class 、 Properties and methods , This is class inheritance .

The inherited class can realize the following functions ：

1. Inherited the methods of the original class , And can be modified

2. Add new methods

3. Add a new data member

While realizing the above functions, certain rules must be met ：

1. Subclasses inherit all data members and methods of the parent class

2. Subclasses can add new data members and methods

3. Subclasses can override data members and methods in the base class

4. If a method is overridden , It must maintain parameters consistent with the original definition of the base class

5. Subclasses can be passed through super Operator to reference methods and members in the parent class

6. Be declared local Data members and methods of can only be visible to themselves , Not visible to both external and subclasses ; Yes, the statement is protected Data members and methods of , Invisible to the outside , Visible to itself and subclasses .

Inheritance and subclasses

Previously defined classes Packet, You can enter — Step extension to form a new class LinkedPacket. adopt extends,LinkedPacket Inherit from its parent class Packet, Including inheriting all its members ( Variable / Method ).

class LinkedPacket extends Packet;
	LinkedPacket next;
	function LinkedPacket get_next();
		get_next = next;
	endfunction
endclass

Subclasses can inherit members of the parent class , therefore LinkedPacket The object is also a legal Packet object .
thus , The parent class handle can point to the object of the child class .

LinkedPacket lp = new;
Packet p = lp;

Handles to parent and child classes , The subclass handle can be directly assigned to the parent handle , Subclasses can have member methods with the same name as the parent class , A child class can have a member variable with the same name as the parent class .

super

super Is the member used to access the current object and its parent class . Especially if the member of the subclass has the same name as the member of the parent class , Then you need to use super Specify its parent class members to access , Instead of the default subclass member .

class Packet; // base class
	integer value;
	function integer delay();
		delay = value * value;
	endfunction
endclass
class LinkedPacket extends Packet; //derived class
	integer value ;
	function integer delay();
		delay = super.delay ()+ value * super.value;
	endfunction
endclass

Use of the bag

The definition of package

In order to make it possible to work in multiple modules （ Hardware ） Or class ( Software ） Share user-defined types between ,SV Added package (package) .
The concept of package refers to VHDL, User defined types such as class 、 Method 、 Variable 、 Structure 、 Enumeration classes can be found in package…endpackage In the definition of .

Export the contents of the package

module、interface、class You can use the content defined or declared in the package .

• You can use the index of the field :: Number directly refers to .

  definitions::parameter
  definitions::instruction_t inst
  

• You can specify to index some types defined in the package to the specified domain .

  module M;
  	import definitions::instruction_t;
  	instruction_t inst;
  endmodule
  

• Through wildcards * To import all categories in the package into the specified domain .

  module M;
  	import definitions::*;
  	instruction_t inst;
  endmodule
  

  Distinction between packages and libraries

  package This container can be used to isolate types .package The significance of is to make the software （ class 、 type 、 Such method ） Encapsulated in different domains , To isolate from the global domain .

  Libraries are compiled products , Hardware ( module、interface、program） Will be compiled into the library , If you don't specify a compiler , Will be compiled into the default library . The library can accommodate hardware types , It can also accommodate software types , For example, class 、 Methods and packages .

  Packages can only contain software types, such as classes 、 Methods and parameters .

reference

1. Verification of West circuit department PPT