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Class Inheritance with `extends`: Code Examples

Code Examples for Class Inheritance with `extends`.

Code examples

Basic extends plus super.new constructor chain

systemverilog
class txn_base;
  rand bit [31:0] addr;

  function new(bit [31:0] addr = '0);
    this.addr = addr;
  endfunction
endclass

class burst_txn extends txn_base;
  rand int unsigned beats;

  function new(bit [31:0] addr = '0, int unsigned beats = 1);
    super.new(addr);
    this.beats = beats;
  endfunction
endclass

module tb;
  initial begin
    burst_txn t = new(32'h1000_0040, 8);
    $display("addr=%08h beats=%0d", t.addr, t.beats);
  end
endmodule

The derived constructor initializes inherited addr by explicitly calling super.new(addr). Without that call, base initialization policy can be bypassed.

Single inheritance with composition for extra capability

systemverilog
class qos_policy;
  int unsigned priority;

  function new(int unsigned priority = 0);
    this.priority = priority;
  endfunction
endclass

class packet_base;
  rand bit [31:0] addr;
  qos_policy qos;

  function new();
    qos = new(3);
  endfunction
endclass

class noc_packet extends packet_base;
  rand bit [7:0] vc;

  function new();
    super.new();
    vc = 0;
  endfunction
endclass

The class gets one inheritance chain (packet_base -> noc_packet) while qos behavior is attached as a composed helper object, which is the idiomatic alternative to multiple inheritance.

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