toster_dynamic_cast_example.cpp

#include <vector>
#include <iostream>

class Fruit{
public:
    std::string variety;
public:
    std::string virtual GetVariety() { return variety; };
};

class Apple : public Fruit{
public:
    Apple(std::string variety) { this->variety = variety; };
};

class Pear : public Fruit{
public:
    Pear(std::string variety) { this->variety = variety; };
};

template <class T>
std::vector<T> GetSelectedFruits(std::vector<Fruit*> fruits){
    std::vector<T> result;

    for(size_t i = 0; i < fruits.size(); ++i) {
        T fruit = dynamic_cast<T>(fruits[i]);
        if(!fruit) continue;

        result.push_back(fruit);
    }

    return result;
}

int main(){
    std::vector<Fruit*> fruits;
    fruits.push_back(new Apple("Macintosh"));
    fruits.push_back(new Pear("Bartlett"));
    fruits.push_back(new Apple("Fuji"));
    fruits.push_back(new Pear("Concorde"));
    fruits.push_back(new Apple("Gala"));

    std::vector<Apple*> apples = GetSelectedFruits<Apple*>(fruits);

    std::cout << "the count of apples: " << apples.size() << std::endl;
    for(size_t i = 0; i < apples.size(); ++i) {
        std::cout << apples[i]->GetVariety() << std::endl;
    }
}