类中的重载运算符，并返回对私有值的引用

Question

Example class I'm using:

class Vector
{
double val[3];
public:
double & operator [] (const unsigned int & index) {return this->val[index];};
}

Then I call it like:

Vector Example;
Example[0]=5;

Is using operator overloading like this correct or it is against encapsulation and I should use something different? I'm using reference to private value here and I'm not sure about this implementation.

Answer 1

Good so far... You also need one that can read from const objects. Also, there's no reason to pass an array index by const&. Also also, this-> is implicit. Look at the member function signatures for std::vector<> . In particular operator[] . Push request...

class Vector
{
    double val[3];
  public:
    double& operator [] (size_t index) {return val[index];};
    const double& operator [] (size_t index) const {return val[index];};
};

Answer 2

This is a leak in your abstraction. It exposes the fact you have actual double s that can be read from or written to.

If you later wanted to change those double s into a remote immediate network connection data or stored in a database, you would be forced to add breaking changes to your interface.

That being said:

It is worth it. You probably will never modify this type to do something that insane, and there are significant compile, design and runtime overheads to unlimited abstraction.

Abstraction and encapsulation serve a purpose and have a cost.

std::vector<bool> 's operator[] is an example of what you can do when reference return types are not ok. There it is used to return sub-byte elements. Note that it is widely considered a design error.