CODEWITHSUNDEEP
c++templatescasting
user64141
user64141

Reputation: 5331

Downcasting template typename object in C++

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
        }
    */
}

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.

Upvotes: 1

Views: 243

Answers (1)

rocambille
rocambille

Reputation: 15996

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
}

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
}

Upvotes: 5

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