在C ++中下转换模板类型名对象 [英] Downcasting template typename object in C++

问题描述

我在一个C ++应用程序中有以下函数，它被称为许多不同的时间：

I have the following function in a C++ application that is called many different times:

template<typename The_ValueType>
void
handleObject(The_ValueType const &the_value)  //unchangable function signature
{ 
    /*
        //Pseudo Java code (not sure how to implement in C++)
        if (the_value instanceof Person){
            Person person = (Person) the_value      
            //do something with person
        }
        if (the_value instanceof Integer){
           int theInt = (Integer) the_value
           //do something with int
        }
    */
}

我需要从the_value对象打印出一些调试信息。不幸的是，我来自Java / JavaScript背景，我非常低效和不可知的C ++。当我尝试在C ++中向下转换，我不断收到错误dynamic_cast的无效目标类型。如何实现伪Java代码列出？基本上，我只需要知道如何做downcast，对象是一个原始或对象。我撕开我的头发，试图理解指针和铸造，任何指导都会完全赞赏。

I need to print out some debugging information from the "the_value" object. Unfortunately, I'm from a Java/JavaScript background, and I'm horribly inefficient and unknowledable with C++. When I try to downcast in C++, I keep getting the error "invalid target type for dynamic_cast". How can implement the "Pseudo Java code" listed? Basically, I just need to know how to do the downcast, be the object a primitive or an object. I'm ripping my hair out trying to understand pointers and casting, and any guidance would be thoroughly appreciated.

推荐答案

这里没有关于downcasting的内容。您应该使用模板专业化：

There is nothing about downcasting here. You should use template specialization:

template<typename The_ValueType>
void
handleObject(const The_ValueType &the_value)
{ 
    // default implementation: do nothing or something else
}

template<>
void
handleObject<Person>(const Person &the_value)
{ 
    //do something with the_value as Person
}

template<>
void
handleObject<int>(const int &the_value)
{ 
    //do something with the_value as int
}

或者更好的是，如果所有类型都已知，您可以使用重载：

Or even better if all types are known, you can use overloading:

void handleObject(const Person &the_value)
{ 
    //do something with the_value as Person
}

void handleObject(const int &the_value)
{ 
    //do something with the_value as int
}

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