返回不可变指针向量的函数的C ++语法

Question

I have the following c++ function on MyClass:

class MyClass {
public:
    std::vector<MyObject*> getVector();
};

I want to make sure objects that grab this collection don't modify the collection or the contents. What is the appropriate c++ const usage to acheive this?

Edit : by "contents" I mean both the pointers and what they point to.

Answer 1

std::vector<const MyObject *> getVector();

or

const std::vector<const MyObject *> &getVector();

should do the trick. You don't need the pointers to be constant, only the MyObject instances they are pointing to and the std::vector object (if returning a reference), so the vector won't alter its state and any referenced item won't be exposed as non-const.

Answer 2

On the side note, std::vector<MyObject*> getVector() will return a copy of that vector, which in terms of OOP principles (encapsulation) is a desirable behaviour:

A call to this getter will not allow to mutate the state of MyClass instance.

Of course perfomance-wise that is poor design, unsless you actually need to return a copy (rather strange specification for a getter). That is why you should return a reference to const object , which in the same time allows returning the object itself (no copying) while disallowing its mutation.

Answer 3

Not sure whether it's correct or not. I just use

class MyClass {
  std::vector<MyObject*> my_objects_;
 public:
  const std::vector<const MyObject*> &getVector() {
    return *reinterpret_cast<const std::vector<const MyObject *> *>(&my_objects_);
  }
};

to do the trick.