[英]Templated class unknown type over multiple layers
I've got following class Foo and FooBase: 我有以下Foo和FooBase类:
class FooBase
{
public:
virtual void A() = 0;
};
template <class T>
class Foo : public FooBase
{
public:
virtual void A() {}
private:
T mT;
};
FooBase
is here to have a instance without needing to know the type, so I can do s.th. FooBase
在这里有一个实例,不需要知道类型,所以我可以做某事。 like this: 像这样:
FooBase *foo = new Foo<int>();
Pretty standard. 很标准。 Now the issue: I want to bring the same thing to the next level.
现在的问题是:我想将同一件事带入一个新的高度。
So I've got the class: 所以我上了课:
template <class T>
class Bar : public Foo<T>
{
public:
virtual void B() {}
};
And can of course use: 当然可以使用:
Bar<int> *bar = new Bar<int>();
Except I don't know the type of the template class. 除了我不知道模板类的类型。 So initial idea was to do the following:
因此,最初的想法是执行以下操作:
class BarBase : public FooBase
{
public:
virtual void B() {}
};
template <class T>
class Bar : public BarBase, Foo<T>
{
};
So I can do the following: 因此,我可以执行以下操作:
BarBase *bar = new Bar<int>();
For obvious reasons this doesn't work - the question is now: How to get s.th. 由于明显的原因,这是行不通的-现在的问题是:如何获得某事。 like this to work?
像这样工作吗?
You can solve this issue with virtual inheritance . 您可以使用虚拟继承解决此问题。 This feature assures that there is only one instance of your virtually-inherited base class when you instantiate a subclass.
此功能可确保在实例化子类时,虚拟继承的基类只有一个实例。 For your example, this would look like:
以您的示例为例:
class FooBase
{
public:
virtual void A() = 0;
};
template <class T>
class Foo : public virtual FooBase
// ^^
{
public:
virtual void A() {}
private:
T mT;
};
class BarBase : public virtual FooBase
// ^^
{
public:
virtual void B() {}
};
template <class T>
class Bar : public BarBase, Foo<T>
{
};
Now you can happily create instances like you wanted: 现在,您可以愉快地创建所需的实例:
BarBase *bar = new Bar<int>();
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