我有一组实现奇怪的重复模板模式的类。但是,诀窍在于基类需要返回子类的实例。这是一个例子:

template <typename SubType>
class ArithmeticBase
{
public:
    template <typename OtherType>
    const Addition operator+(const OtherType &other)
        {return Addition(get_subclass(), other);}

    // ...
    // Operators for subtraction, multiplication, division, ...

private:
    const SubType &get_subclass() const
        {return *static_cast<const SubType*>(this);}
};

template <typename OperatorType1, typename OperatorType2>
class Addition : ArithmeticBase<Addition<OperatorType1, OperatorType2>>
{
public:
    Addition(const OperatorType1 &op1, const OperatorType2 &op2)
        : op1(op1)
        , op2(op2)
    {}

private:
    const OperatorType1 &op1;
    const OperatorType2 &op2;
};

// ...
// Additional classes for subtraction, multiplication, division, ...


编译失败,因为Addition类在ArithmeticBase类中使用之前未定义:

arithmetic.cpp:6:8: error: unknown type name 'Addition'
        const Addition operator+(const OtherType &other)
              ^


我该如何解决?

最佳答案

您可以在基类之前转发声明Addition

template <typename OperatorType1, typename OperatorType2>
class Addition;
template <typename SubType>
class ArithmeticBase
{
...
};


这使编译器在定义它之前就知道存在类型Addition

10-06 01:03