为什么operator =不会从模板类继承 [英] Why operator = doesn't get inherited from a template class

问题描述

我有以下模板代码：

class ClassName{};

template <class T>
class TemplatePtr
{
public:
    void operator=(T* p)
    {

    }
};

class TemplatePtr_ClassName: public TemplateePtr<ClassName>
{
public:
    ~TempaltePtr_ClassName();
};


void Test()
{
    TemplatePtr_ClassName data;
    data = new ClassName;
}

但编译失败并显示错误讯息（VS2008）：

but compile fails with error message (VS2008):

错误C2679：binary'='：无操作符，它接受类型为>> ClassName *'的右手操作数或没有可接受的转换）

error C2679: binary '=' : no operator found which takes a right-hand operand of type >>'ClassName *' (or there is no acceptable conversion)

为什么它不工作，在模板基类中？

Why it won't work as I have defined an operator in the template base class?

推荐答案

operator =始终被派生类实现隐藏，除非提供了显式使用声明。对于类模板和普通类都是如此。

operator = is always hidden by the derived class implementation unless explicit using declaration is provided. This is true for both class templates and ordinary classes.

BTW，你的statement =的声明是非标准的。它通常被声明为类'A'。

BTW, your declaration of operator= is very nonstandard. It is usually declared so for a class 'A'.

A& operator=(A const &);

这里是可能是你正在寻找（和编译）的东西

Here is something that may be what you are looking for (and compiles)

template <class T> 
class TemplatePtr 
{ 
public: 
    TemplatePtr& operator=(TemplatePtr const &) 
    {return *this;} 
}; 

template<class T>
class TemplatePtr_ClassName: public TemplatePtr<T> 
{ 
public:
   ~TemplatePtr_ClassName(){};
   TemplatePtr_ClassName& operator=(TemplatePtr_ClassName const &that){
      TemplatePtr<T>::operator=(that);        // invoke base class assignment operator
      return *this;
   }
}; 


int main() 
{ 
    TemplatePtr_ClassName<int> data; 
    data = *new TemplatePtr_ClassName<int>; 
    // delete stuff
} 

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