[英]Adding methods to template specialization
I have a templated C++ class that exposes a number of methods, eg 我有一个模板化的C ++类,它暴露了许多方法,例如
template<int X, int Y>
class MyBuffer {
public:
MyBuffer<X,Y> method1();
};
Now, I want to expose additional methods to this class if X == Y. I have done this by subclassing MyBuffer, 现在,如果X == Y,我想向这个类公开其他方法。我通过继承MyBuffer来完成这个,
template<int X>
class MyRegularBuffer : public MyBuffer<X,X> {
public:
MyRegularBuffer method2();
};
Now, the problem is that I want to be able to do eg 现在,问题是我希望能够做到,例如
MyRegularBuffer<2> buf = ...
MyRegularBuffer<2> otherBuf = buf.method1().method2();
But I am not sure how to accomplish this. 但我不知道如何做到这一点。 I tried to think of copy constructors, conversion operators, etc, but my C++ skills are unfortunately a bit rusty.
我试着想到复制构造函数,转换运算符等,但遗憾的是我的C ++技能有点生疏。
EDIT: I should add that creation of these objects is relatively cheap (and also, it won't happen a lot), which means it would be OK to do something like this: 编辑:我应该补充说,这些对象的创建相对便宜(而且,它不会发生很多),这意味着可以做这样的事情:
MyRegularBuffer<2> buf = ...
MyRegularBuffer<2> temp = buf.method1(); // Implicit conversion
MyRegularBuffer<2> otherBuf = temp.method2();
The question is then, how can I define the conversion like that. 那么问题是,如何定义这样的转换。 The conversion operator needs to be in MyBuffer, I think, but I want it to be available only if X==Y.
我认为转换运算符需要在MyBuffer中,但我希望它只有在X == Y时才可用。
You don't need a separate class to represent the special behaviour. 您不需要单独的类来表示特殊行为。 Partial specialization allows you to treat some of the MyBuffer <X,Y> cases specially and give them extra methods.
部分专业化允许您专门处理一些MyBuffer <X,Y>案例并为其提供额外的方法。
Keep your original declaration of MyBuffer<X,Y> and add this: 保留MyBuffer <X,Y>的原始声明并添加:
template<int Y>
class MyBuffer<Y, Y> {
public:
MyBuffer<Y,Y> method1();
MyBuffer<Y,Y> method2();
};
MyBuffer<1,2> m12; m12.method2(); // compile fail, as desired, as it doesn't have such a method because 1 != 2
MyBuffer<2,2> m22; m22.method2(); // compile success
Edit: my final lines weren't very useful after all, as pointed out by Georg in the comments, so I've deleted them. 编辑:我的最后几行毕竟不是很有用,正如Georg在评论中指出的那样,所以我删除了它们。
I'd go for CRTP here: 我在这里找CRTP :
template<int X, int Y, class Derived>
struct MyBufferBase {
// common interface:
Derived& method1() { return *static_cast<Derived*>(this); }
};
template<int X, int Y>
struct MyBuffer : MyBufferBase<X, Y, MyBuffer<X,Y> > {
// basic version
};
template<int X>
struct MyRegularBuffer : MyBufferBase<X, X, MyRegularBuffer<X> > {
// extended interface:
MyRegularBuffer& method2() { return *this; }
};
It's possible to do what you want if method1
and method2
return a reference to *this
. 如果
method1
和method2
返回对*this
的引用,则可以执行您想要的操作。 Otherwise, you're going to need to either do a conversion, or make method1
virtual. 否则,您将需要进行转换,或将
method1
设为虚拟。
The trick is to have a MyRegularBuffer::method1
that calls MyBuffer::method1
, then a way to convert the resultant MyBuffer<X,X>
into a MyRegularBuffer<X>
: 诀窍是让
MyRegularBuffer::method1
调用MyBuffer::method1
,然后将结果MyBuffer<X,X>
转换为MyRegularBuffer<X>
:
template<int X>
class MyRegularBuffer : public MyBuffer<X,X>
{
public:
MyRegularBuffer<X>()
{}
MyRegularBuffer<X>(MyBuffer<X,X>)
{
// copy fields, or whatever
}
MyRegularBuffer<X> method2();
MyRegularBuffer<X> method1()
{
MyRegularBuffer<X> ret(MyBuffer<X,X>::method1());
return(ret);
}
};
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