SYSTEM VERILOG - Interview questions

This was asked in one of the interviews I faced with a product company.

Looks simple at first glance, but sometimes these questions might catch you off-guard.

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class base; int a; function new ( int val ); a = val; endfunction function void display(); $display("BASE:: A:%0d",a); endfunction endclass class derived extends base; function new (int val); super.new(19); a = val; endfunction function void display(); $display("DERIVED:: A:%0d",a); endfunction endclass module top; base b; derived d; initial begin b = new(10); d = new(20); b.display(); d.display(); b = d; b.display(); d.display(); end endmodule: top

Guess the output in the following scenarioes.

1. Without call to super.new(19) in line 19.
2. With call to super.new(19)
1. Without virtual method in Base class
1. As-it-is
2. With one line ' int a; '  added to the derived class code
2. With adding virtual keyword in front of display() in Base class
1. Repeat 2.1.1 and 2.1.2

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Answers :

1. Error-[SV-SNCIM] Super new call is missing

testbench.sv, 17
$unit
Base class constructor specification is missing in derived class 'derived'.
Please add <base class>::new arguments to 'extends' specification or add
call to 'super.new' in <derived class>::new.

1 error

2.1.1  - Without virtual and without < int a; > in base class

Compiler version Q-2020.03-SP1-1; Runtime version Q-2020.03-SP1-1; Jan 12 07:21 2021
BASE:: A:10
DERIVED:: A:20
BASE:: A:20
DERIVED:: A:20

2.1.2 - Without virtual and with < int a; > in base class

Compiler version Q-2020.03-SP1-1; Runtime version Q-2020.03-SP1-1; Jan 12 07:21 2021
BASE:: A:10
DERIVED:: A:20
BASE:: A:19
DERIVED:: A:20

2.2.1 With virtual and without < int a; > in base class

Compiler version Q-2020.03-SP1-1; Runtime version Q-2020.03-SP1-1; Jan 12 07:22 2021
BASE:: A:10
DERIVED:: A:20
DERIVED:: A:20
DERIVED:: A:20

2.2.2 With virtual and with < int a; > in base class

Compiler version Q-2020.03-SP1-1; Runtime version Q-2020.03-SP1-1; Jan 12 07:23 2021
BASE:: A:10
DERIVED:: A:20
DERIVED:: A:20
DERIVED:: A:20