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Master Software Design Patterns and Architecture in C++

Solution: Type Erasure

Explore the concept of type erasure in C++ by understanding how to use templates and shared pointers for polymorphic object storage. Learn to apply this idiom to manage different object types in a unified way, improving your software design and code flexibility.

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Solution

C++
#include <iostream>
#include <memory>
#include <string>
#include <vector>
class Object {
	
 public:
    template <typename T> 
    explicit Object(const T& obj): object(std::make_shared<Model<T>>(std::move(obj))){}
      
    std::string getName() const { 
        return object->getName(); 
    }
	
    struct Concept {
       virtual ~Concept() {}
	   virtual std::string getName() const = 0;
    };
    template< typename T > 
    struct Model : Concept {
       explicit Model(const T& t) : object(t) {}
	   std::string getName() const override {
		   return object.getName();
	   }
     private:
       T object;
    };
    std::shared_ptr<const Concept> object;
};
void printName(std::vector<Object> vec){
    for (auto v: vec) std::cout << v.getName() << '\n';
}
struct Bar {
	std::string getName() const {
	    return "Bar";
	}
};
struct Foo {
	std::string getName() const {
	    return "Foo";
	}
};
int main(){
	
	std::cout << '\n';
	
	std::vector<Object> vec{Object(Foo()), Object(Bar())};
	
	printName(vec);
	
	std::cout << '\n';
}

Explanation

  • Lines 6–32: We defined the Object class, which has a templated constructor that takes in a constant reference to an object of type T. This constructor creates a std::shared_ptr to a Model object, which is a member of the Object class and is defined on line 21. The Model struct has a templated constructor that takes in a constant reference ...