Simple value object example in C++

value_object.cpp

/*
    Ukázka jak implementovat jednoduchý *value object*.
 */

#include <string>
#include <stdexcept>
#include <iostream>

template<typename T>
class SingleValueObject 
{   
  public:
    
    /*! 
         \brief The value constructor.
     */
    constexpr SingleValueObject(T const &value) : _value(value) { }

    /*! 
        \brief Gets the stored value.  
     */
    inline T value() const noexcept { return _value; }
  
  protected:
    
    virtual ~SingleValueObject() { }

  private:

    T const _value;
};

struct Email final : SingleValueObject<std::string>
{   
    /*!
        \brief The value constructor.
     */
    Email(std::string const &value) : SingleValueObject(validated(value)) { }

    /*! 
         \brief Validates the input value.
     */ 
    static std::string validated(const std::string &value) 
    {
        if (!value.size()) {
            throw std::invalid_argument("Value cannot be empty!");
        }
        return value;
    }
};

int main()
{
    const Email e1("[email protected]");
    const Email e2("[email protected]");

    std::cout << e1.value() << std::endl;
    std::cout << e2.value() << std::endl;

    try {
        const Email e3("");
    }
    catch (std::exception const &e) {
        std::cout << e.what();
    }

    try {
        const Email e4(nullptr);
    }
    catch (std::exception const &e) {
        std::cout << e.what();
    }

    // Rovnost je v C++ ve výchozím stavu strukturální.

    std::cout << (e1.value() == e2.value()) << std::endl;
}