static屬性一般是在編譯的時候就已經(jīng)分配了內(nèi)存，并被這個類的所有實例共享，

也就是在仿真時刻0之前就已經(jīng)完成了靜態(tài)屬性的內(nèi)存分配。

但是，參數(shù)化類中的靜態(tài)屬性可能有所區(qū)別。參數(shù)化類中的靜態(tài)屬性（參數(shù)化）是在參數(shù)初始化的時候才會分配。

 // Class with parameters
 class with_param #(type T = int);
 static T static_with_p;
 endclass
 
 // Class without Parameters
 class without_param;
 static int static_wo_p;
 endclass
 
 module top;
 initial begin
 $display("static_wo_p = %0d", without_param :: 
static_wo_p);
 $display("static_with_p = %0d", with_param :: 
static_with_p);
 end
 endmodule: top

在上面的兩個class中，一個包含parameter (with_param)，還有一個不包含parameter(without_param).

在各自class中，我們都聲明了靜態(tài)屬性。在訪問靜態(tài)屬性“static_wo_p”時沒有問題，而在訪問靜態(tài)屬性
“static_with_p”時，編譯器會報錯（Error或者Warning）：

Warning-[PCSRMIO] Class scope used outside of class
testbench.sv, 59
"with_param::static_with_p"
An unspecialized class scope '::' reference was seen.  To access
a static member of the default specialization outside the class
'with_param', use 'with_param#( )::' instead. This will be an
error in a future release.

需要修改成下面這樣的寫法才能編譯通過。

$display("static_with_p = %0d", with_param # ( ) :: static_with_p);

下面這個例子更能夠展示參數(shù)化類中的靜態(tài)屬性和非參數(shù)類中的靜態(tài)屬性的區(qū)別：

class with_param #(type T = int);
static T counter = 2;
function new;
counter++;
endfunction: new
endclass: with_param


class with_param_extend extends with_param #(real);
endclass: with_param_extend


typedef with_param #(byte) s_byte;
s_byte S1 = new( );
s_byte S2 = new( );
with_param S3 = new( );
with_param #(bit[2:0]) S4 = new( );
with_param_extend S5 = new( );
initial begin
$display ("Counter value of S1 instance = %0d", with_param 
#(byte)::counter);
$display ("Counter value of S2 instance = %0d", s_byte:: 
counter);
$display ("Counter value of S3 instance = %0d", with_param 
#()::counter);
$display ("Counter value of S4 instance = %0d", with_param 
#(bit[2:0])::counter);


$ d i s p l a y ( " C o u n t e r 
value of S5 instance =%0d",with_param_extend::counter);
end

仿真log:

Counter value of S1 instance = 4
Counter value of S2 instance = 4
Counter value of S3 instance = 3
Counter value of S4 instance = 3
Counter value of S5 instance = 3.000000
 V C S S i m u l a t i o n R e p o r t

上面的例子中S1、S2、S3、S4、S5中的參數(shù)T分別被覆蓋成byte、byte、int、bit[2:0]、real，所以只有S1（s_byte）和S2（s_byte）中的靜態(tài)屬性counter彼此共享。

參數(shù)類的擴(kuò)展類

class class1 #(type T = int);
 ….
endclass
 
class class2 #(type P = real) extends class1;


class class3 #(type P = real) extends class1 #(integer);


class class4 #(type P = real) extends class1 #(P);

上面是一個參數(shù)化類的擴(kuò)展類示例，class1是一個參數(shù)化類，參數(shù)T默認(rèn)為"int"。

class2增加了一個參數(shù)P，此時參數(shù)T為默認(rèn)的"int"

class3增加了一個參數(shù)P，此時參數(shù)T覆蓋成"integer"

class4增加了一個參數(shù)P，此時參數(shù)T也覆蓋成為P