SystemVerilog将派生的类句柄分配给基类对象
这似乎是我应该可以做的简单的事情，但我想我不完全理解多态性。我从监视器的分析端口获得了一个基类对象，并希望从此基类对象创建一个派生的类对象，然后设置派生类的额外成员（用于覆盖范围）。这样做的最简单方法是什么？
class BasePkt extends uvm_object;
//...
endclass
.
class CovPkt extends BasePkt;
//more members...
endclass
.
task process_pkt();
forever begin
BasePkt base_pkt;
CovPkt cov_pkt;
pkt_ap.get(base_pkt);
cov_pkt = base_pkt; // Compile error
end
endtask
我可以创建一个在COVPKT对象中执行basepkt的深层副本的函数，但这似乎不是正确的事情。由于COVPKT包含Basepkt的所有成员，因此我为什么不能将其分配给Basepkt类，然后让不在Basepkt中的CoVPKT成员成为其默认值？
This seems like a simple thing I should be able to do but I guess I don't fully understand polymorphism. I get a base class object from a monitor's analysis port and want to create a derived class object from this base class object, and then set extra members of the derived class (for coverage). What's the simplest way to go about doing this?
class BasePkt extends uvm_object;
//...
endclass
.
class CovPkt extends BasePkt;
//more members...
endclass
.
task process_pkt();
forever begin
BasePkt base_pkt;
CovPkt cov_pkt;
pkt_ap.get(base_pkt);
cov_pkt = base_pkt; // Compile error
end
endtask
I could create a function that performs a deep copy of BasePkt into a CovPkt object, but that doesn't seem like the right thing to do. Since CovPkt contains all the members of BasePkt, why can't I just assign it to a BasePkt class and then let the members of CovPkt that aren't in BasePkt be their default value?
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因为你不能。
当您从一个类变量进行分配到另一个类变量时，您将复制一个类句柄，而不是类对象本身。句柄是对构造对象的参考。在您的示例中，我假定
base_pkt包含basepktclass Object的句柄。该对象仅包含保持basepkt成员的空间。如果允许您直接将basepkt对象分配到covpkt类变量，则引用covpkt成员将在该空间之外。您需要首先构造
covpkt类对象，然后复制base_pkt成员是正确的。但是，由于您正在使用UVM，因此一种更好的方法是通过使用工厂在监视器中的源中简单地创建covpkt。您可以使用covpkt覆盖basepkt，而无需更改监视器中的任何代码。然后，您将能够在任务中执行动态铸件。您可能想在。
Because you can't.
When you make an assignment from one class variable to another, you are copying a class handle, not the class object itself. A handle is a reference to a constructed object. In your example, I presume
base_pktcontains a handle to aBasePktclass object. The object only contains the space to hold theBasePktmembers. If you were allowed to directly make an assignment of aBasePktobject to aCovPktclass variable, references toCovPktmembers would be outside that space.You were correct in needing to construct a
CovPktclass object first, and then copying thebase_pktmembers. However, since you are using the UVM, a better approach is to simply create aCovPktat the source in the Monitor by using the factory. You can overrideBasePktwithCovPktwithout changing any code in the Monitor. Then you will be able to perform a dynamic cast in your task.You might want to take a look at my course on SystemVerilog OOP for UVM.