NEW in SystemVerilog

	class base;
	function new ();
	$display ("%m from base class new");
	endfunction : new
	endclass : base
	class child extends base;
	function new ();
	// Implicitly super.new is called by compiler
	$display ("%m from child class new");
	endfunction : new
	endclass : child
	module top();
	base b;
	child c;
	initial begin
	c = new();
	end
	endmodule : top
	//Output:
	// $unit::\base::new from base class new
	// $unit::\child::new from child class new
	// Q. What is the return type of the constructor?
	// A1. On the return “type” it is different from other functions.
	// It is very “adaptive in nature”
	// i.e. it returns what the LHS requires.
	// i.e. it returns an object of the type of the handle that appears on the LHS.
	// Hence there is NO return type declared for this special function.
	// As per SystemVerilog LRM,
	// If a class does not provide an explicit user-defined new method,
	// an implicit new method shall be provided automatically.
	// The new method of a derived class shall first call its base class constructor super.new().
	// A super.new call shall be the first statement executed in the constructor.
	// This is because the superclass shall be initialized before the current class and,
	// if the user code does not provide an initialization,
	// the compiler shall insert a call to super.new automatically.

view raw sv_new1.sv hosted with ❤ by GitHub

	class base;
	function new ();
	$display ("%m from base class new");
	endfunction : new
	endclass : base
	class child extends base;
	function new ();
	super.new(); //Explicitly super.new called
	$display ("%m from child class new");
	endfunction : new
	endclass : child
	module top();
	base b;
	child c;
	initial begin
	c = new();
	end
	endmodule : top
	//Output:
	// $unit::\base::new from base class new
	// $unit::\child::new from child class new

view raw sv_new2.sv hosted with ❤ by GitHub

	class base;
	function new (int unsigned id);
	$display ("%m from base class new");
	endfunction : new
	endclass : base
	class child extends base;
	function new ();
	$display ("%m from child class new");
	endfunction : new
	endclass : child
	module top();
	base b;
	child c;
	initial begin
	c = new();
	end
	endmodule : top
	// There is an error: recall that the base’s new is always called,
	// but now the “id” argument is NOT provided for the IMPLICIT call to new.
	//Output:
	//Error-[SV-SNCIM] Super new call is missing
	//top2.sv, 7
	//$unit
	// Base class constructor specification is missing in derived class 'child'.
	// Please add <base class>::new arguments to 'extends' specification or add
	// call to 'super.new' in <derived class>::new.
	// Below is the possible ways to fix this error.
	// 1. Add default arguement in constructor of base (super) class.
	// 2. Explicitly call super.new with required arguements.

view raw sv_new3.sv hosted with ❤ by GitHub

	class base;
	function new (int unsigned id = 1);
	$display ("%m from base class new");
	endfunction : new
	endclass : base
	class child extends base;
	function new ();
	$display ("%m from child class new");
	endfunction : new
	endclass : child
	module top();
	base b;
	child c;
	initial begin
	c = new();
	end
	endmodule : top
	//Output:
	// $unit::\base::new from base class new
	// $unit::\child::new from child class new
	// Q: Can we declare constructor as virtual?
	// A1. In the above code we just added an argument called “id” to the base class constructor.
	// In the derived we decided to “forget” about it.
	// If it was a “virtual” function, as per the semantics, this would be illegal
	// i.e. the function prototype/signature must remain same across inheritance.
	// However the re-definition of new in derived class is just fine.
	// A2. Constructor of a class is never and ever extended by a derived.
	// A3. As mentioned in A1, function signature of derived class's constructor can be
	// a different then signature of base class's constructor.
	// However signature must remain same across inheritance.

view raw sv_new4.sv hosted with ❤ by GitHub

	class base;
	function new (int unsigned id);
	$display ("%m from base class new");
	endfunction : new
	endclass : base
	class child extends base;
	function new ();
	super.new(1);
	$display ("%m from child class new");
	endfunction : new
	endclass : child
	module top();
	base b;
	child c;
	initial begin
	c = new();
	end
	endmodule : top
	//Output:
	// $unit::\base::new from base class new
	// $unit::\child::new from child class new
	// When using the super within new, super.new shall be the first statement executed in the constructor.
	// This is because the superclass shall be initialized before the current class and,
	// if the user code does not provide an initialization,
	// the compiler shall insert a call to super.new automatically.

view raw sv_new5.sv hosted with ❤ by GitHub