Un par de pensamientos sobre captadores y definidores en C ++

Este artículo trata sobre captadores y definidores en C ++. Pido disculpas, pero no estamos hablando de corrutinas. Por cierto, la segunda parte sobre los grupos de subprocesos aparecerá en un futuro próximo.

TL; DR : los captadores y definidores no son muy adecuados para objetos estructurados.

Introducción

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, :

class PersonGettersSetters {
  public:
    std::string getLastName() const { return m_lastName; }
    std::string getFirstName() const { return m_firstName; }
    int getAge() const {return m_age; }
    
    void setLastName(std::string lastName) { m_lastName = std::move(lastName); }
    void setFirstName(std::string firstName) { m_firstName = std::move(firstName); }
    void setAge(int age) {m_age = age; }
  private:
    int m_age = 26;
    std::string m_firstName = "Antoine";
    std::string m_lastName = "MORRIER";    
};
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

.

struct Person {
    int age = 26;
    std::string firstName = "Antoine";
    std::string lastName = "MORRIER";
};
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

. , , .

. Person (firstName



), (lastName



) (age



). , , .

std::string getPresentation(const PersonGettersSetters &person) {
  return "Hello, my name is " + person.getFirstName() + " " + person.getLastName() +
  " and I am " + std::to_string(person.getAge());
}

std::string getPresentation(const Person &person) {
  return "Hello, my name is " + person.firstName + " " + person.lastName + " and I am " + std::to_string(person.age);
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

30% , . ? - . , . person.getFirstName()



; person.firstName



.

, noop.

, . ​​ , . :

class PersonGettersSetters {
  public:
    const std::string &getLastName() const { return m_lastName; }
    const std::string &getFirstName() const { return m_firstName; }
    int getAge() const {return m_age; }
    
    void setLastName(std::string lastName) { m_lastName = std::move(lastName); }
    void setFirstName(std::string firstName) { m_firstName = std::move(firstName); }
    void setAge(int age) {m_age = age; }
  private:
    int m_age = 26;
    std::string m_firstName = "Antoine";
    std::string m_lastName = "MORRIER";    
};

      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, , , ? , .

PersonGettersSetters make() {
    return {};   
}

int main() {
    auto &x = make().getLastName();
     
    std::cout << x << std::endl;
    
    for(auto x : make().getLastName()) {
        std::cout << x << ",";   
    }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, . ? , make().getLastName()



?

1. Person.

   
   
   
   
   

2. .

   
   
   
   
   

3. Person.

   
   
   
   
   

! ( ) - , -, .

, ref-qualified



.

class PersonGettersSetters {
  public:
    const std::string &getLastName() const & { return m_lastName; }
    const std::string &getFirstName() const & { return m_firstName; }
    
    std::string getLastName() && { return std::move(m_lastName); }
    std::string getFirstName() && { return std::move(m_firstName); }
    
    int getAge() const {return m_age; }
    
    void setLastName(std::string lastName) { m_lastName = std::move(lastName); }
    void setFirstName(std::string firstName) { m_firstName = std::move(firstName); }
    void setAge(int age) {m_age = age; }
    
  private:
    int m_age = 26;
    std::string m_firstName = "Antoine";
    std::string m_lastName = "MORRIER";    
};
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, . . lvalue



rvalue



( xvalue



, prvalue



).

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, , rvalue



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- const. . move- .

, . , , immutable



<T>. :

1. Constructible
   
   
   
   

   
   
   
   
   

2. immutable
   
   
   
   , assignable
   
   
   
   

   
   
   
   
   

3. copy constructible



move constructible
   
   
   
   

   
   
   
   
   

4. const T
   
   
   
   &, lvalue
   
   
   
   

   
   
   
   
   

5. T
   
   
   
   , rvalue
   
   
   
   

   
   
   
   
   

6. , , *



->
   
   
   
   .

   
   
   
   
   

7. .

   
   
   
   
   

:

#define FWD(x) ::std::forward<decltype(x)>(x)

template <typename T>
struct AsPointer {
    using underlying_type = T;
    AsPointer(T &&v) noexcept : v{std::move(v)} {}
    T &operator*() noexcept { return v; }
    T *operator->() noexcept { return std::addressof(v); }
    T v;
};

template <typename T>
struct AsPointer<T &> {
    using underlying_type = T &;
    AsPointer(T &v) noexcept : v{std::addressof(v)} {}
    T &operator*() noexcept { return *v; }
    T *operator->() noexcept { return v; }
    T *v;
};

template<typename T>
class immutable_t {
  public:
    template <typename _T>
    immutable_t(_T &&t) noexcept : m_object{FWD(t)} {}

    template <typename _T>
    immutable_t &operator=(_T &&) = delete;

    operator const T &() const &noexcept { return m_object; }
    const T &operator*() const &noexcept { return m_object; }
    AsPointer<const T &> operator->() const &noexcept { return m_object; }

    operator T() &&noexcept { return std::move(m_object); }
    T operator*() &&noexcept { return std::move(m_object); }
    AsPointer<T> operator->() &&noexcept { return std::move(m_object); }

    T *operator&() &&noexcept = delete;
    const T *operator&() const &noexcept { return std::addressof(m_object); }

    friend auto operator==(const immutable_t &a, const immutable_t &b) noexcept { return *a == *b; }

    friend auto operator<(const immutable_t &a, const immutable_t &b) noexcept { return *a < *b; }

  private:
    T m_object;
};
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, Person :

struct ImmutablePerson {
    immutable_t<int> age = 26;
    immutable_t<std::string> firstName = "Antoine";
    immutable_t<std::string> lastName = "MORRIER";
};
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

, - . , - , , :

• 3- ( 4-): const lvalue
  
  
  
  , rvalue
  
  
  
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PS: , , . 2 0. , , , .

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