奇怪的方式从BoostCon谈话过载解除引用操作符 [英] Strange way of overloading the dereference operator from a BoostCon talk

问题描述

我在YouTube上观看了一个boostcon演讲，题为现代C ++技术介绍（第一部分）。在分钟22，演讲者显示一个重载解引用操作符的类。

 模板< typename T，
 typename CheckingPolicy = NoChecking，
 typename BadPointerPolicy = BadPointerDoNothing> 
 class pointer_wrapper 
 {
 public：
 pointer_wrapper（）：value_（0）{} 
 explicit pointer_wrapper（T * p）：value_（p）{} 
 
 operator T *（）
 {
 if（！CheckingPolicy :: check_pointer（value_））
 {
 return BadPointerPolicy :: handle_bad_pointer（value_）; 
} 
 else 
 {
 return value_; 
} 
} 
 
 private：
 T * value_; 
}; 
  

我从来没有见过这种重载解引用操作符的方法。为什么没有返回类型，为什么T出现在'operator'关键字后面？
我一直认为重载这个操作符的方法是这样的：

  operator *（）
 {
 // ... 
 return * value_ 
} 
  

如果有人感兴趣，请此处是说话

解决方案

这是隐式转换操作符类型T * 。
n3337 12.3.2 / 1

类X的成员函数，没有带有

形式名的参数

conversion-function-id：

operator conversion-type-id

-id：

type-specifier-seq
conversion-declaratoropt

conversion-declarator： / p>

ptr-operator conversion-declaratoropt

指定从X转换为转换指定的类型-type-id 。这样的函数称为
转换函数。

如果转换函数是成员函数，转换函数（8.3.5）的
类型是function taken no parameter returning conversion-type-id

I was watching a boostcon talk on youtube titled "Introduction to Modern C++ Techniques (Part I)". Around minute 22 the speaker shows a class which overloads the dereference operator.

template<typename T,
         typename CheckingPolicy = NoChecking,
         typename BadPointerPolicy = BadPointerDoNothing>
class pointer_wrapper
{
public:
    pointer_wrapper() : value_(0) {}
    explicit pointer_wrapper(T* p) : value_(p) {}

    operator T*()
    {
        if ( ! CheckingPolicy::check_pointer(value_) )
        {
            return BadPointerPolicy::handle_bad_pointer(value_);
        }
        else
        {
            return value_;
        }
    }

private:
    T* value_;
};

I have never seen this way of overloading the dereference operator. Why is there no return type and why does the T appear after the 'operator' keyword? I always thought the way to overload this operator was like this:

T& operator *()
{
    // ...
    return *value_
}

If anybody is interested, here is the talk

解决方案

It's implicit conversion operator to type T*. n3337 12.3.2/1

A member function of a class X having no parameters with a name of the form

conversion-function-id:

operator conversion-type-id

conversion-type-id:

type-specifier-seq conversion-declaratoropt

conversion-declarator:

ptr-operator conversion-declaratoropt

specifies a conversion from X to the type specified by the conversion-type-id. Such functions are called conversion functions. No return type can be specified.

If a conversion function is a member function, the type of the conversion function (8.3.5) is "function taking no parameter returning conversion-type-id".

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