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package my_package;

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class Register;

  // Properties

  logic [7:0] data;

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  // Methods

  function new (logic[7:0] d = 0); // Constructor

    data = d;

  endfunction

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  task load (logic[7:0] d);

    data = d;

  endtask

endclass

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// Parameterised classes

class Register1 #(parameter n = 8);

  logic [n-1:0] data;

endclass

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class Register2 #(parameter type T);

  T data;

endclass

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// Derived class

class ShiftRegister extends Register;

  extern task shiftleft();

  extern task shiftright();

endclass

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// Out of class method definitions

task ShiftRegister::shiftleft();

  data = data << 1;

endtask

task ShiftRegister::shiftright();

  data = data >> 1;

endtask

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endpackage

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module GRG_class1;

import my_package::*;

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Register accum; // accum stores a handle to an object of class Register

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Register1 #(8) accum1_8 = new;           // 8-bit register

Register1 #(.n(16)) accum1_16 = new;     // 16-bit register

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Register2 #(int) accum2_8 = new;         // int register

Register2 #(bit [7:0]) accum2_16 = new;  // bit[7:0] register

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ShiftRegister SR = new;

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initial begin

  accum = new;    // Create a new Register object; its handle is in accum

  accum.data = 8'h1f;        // Store value in data member

  $display("accum.data = %0h", accum.data);

  accum.load(8'h1f);         // A better way of doing it

  $display("accum.data = %0h", accum.data);

end

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initial begin

  static Register accum1 = new;        // Alternative

  static Register accum2 = new(8'hff); // Initialize

  static Register accum3[10];

  foreach (accum3[i])

    accum3[i] = new;    // Array of 10 Registers

end

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initial begin

  SR.load(8'h55);                      // Inherited method

  $display("SR.data = %0h", SR.data);

  SR.shiftleft;                        // data now has 8’aa

  $display("SR.data = %0h (after shift left)", SR.data);

end

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endmodule

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