typedef class
Table of Contents
A typedefis used to provide a forward declaration of the class.
In some cases, the class needs to be instantiated before the class declaration. In these kinds of situations, the typedef is used to provide a forward declaration of the class.
typedef syntax
typedef class class_name;
typedef examples
Without typedef
In the below example,
There are two classes c1 and c2.
c2 is instantiated inside c1 and c1 inside c2. Both classes need the handle of each other. As execution will happen in sequential order.
Dependency between both the classes leads to a compilation error.
//class-1
class c1;
c2 c; //using class c2 handle before declaring it.
endclass
//class-2
class c2;
c1 c;
endclass
module typedef_class;
initial begin
c1 class1;
c2 class2;
$display("Inside typedef_class");
end
endmodule
Simulator Output
Error-[SE] Syntax error Following verilog source has syntax error : token 'c2' should be a valid type. Please declare it virtual if it is an Interface. "testbench.sv", 6: token is ';' c2 c;
With typedef
The compilation error of the above example can be avoided by using a typedef.
typedef class c2;
//class-1
class c1;
c2 c; //using class c2 handle before declaring it.
endclass
//class-2
class c2;
c1 c;
endclass
module typedef_class;
initial begin
c1 class1;
c2 class2;
$display("Inside typedef_class");
end
endmodule
Simulator Output
Inside typedef_class