Sometimes it is required to have only one object of some classes like configuration classes. For this purpose we create singleton classes. Only one object is created for a singleton class and whenever we try to create a new object, same object is returned.
System verilog does not provide construct to create a singleton class. But we can create it with some manupulations
01.// Filename : singleton.sv
02.// Author : Puneet (er.punit@gmail.com)
03.// Website : http://www.asicguru.com
04.
05.class singleton;
06.int len;
07.
08.static singleton objSingle;
09.
10.local function new (int len=0);
11.this.len = len;
12.endfunction : new
13.
14.function void print_len ();
15.$display("Len is = %d", len);
16.endfunction : print_len
17.
18.static function singleton create (int len=0);
19.if (objSingle == null) begin
20.$display("Object is null creating new object \n");
21.objSingle = new(len);
22.end
23.
24.return objSingle;
25.endfunction : create
26.
27.endclass
28.
29.program main;
30.
31.singleton objSingle1;
32.singleton objSingle2;
33.
34.initial
35.begin
36.objSingle1 = singleton::create ( );
37.objSingle2 = singleton::create ( );
38.
39.$display("Testing Singleton object \n");
40.objSingle2.len = 10;
41.objSingle1.print_len(); // Call print len function
42.objSingle2.print_len(); // Call print len function
43.
44.objSingle1.len = 99;
45.objSingle1.print_len(); // Call print len function
46.objSingle2.print_len(); // Call print len function
47.end
48.
49.endprogram: main
50.
51.
52.
53.
54.//Output
55.Object is null creating new object
56.
57.Testing Singleton object
58.
59.Len is = 10
60.Len is = 10
61.Len is = 99
62.Len is = 99
63.V C S S i m u l a t i o n R e p o r t
