C++ Preventing const methods from changing data through a member pointer or reference

Question

Say I have a simple class like this

class Foo
{
public:
    void foo()const
    {
        str[5] = \'x\';
        obj->changeTheWorld();
        x = 4;
               


        

Answer 1

Well, neither std::reference_wrapper nor std::shared_ptr do not provide const propagation, so they are not more "const-strict" than regular pointer.

I'd recommend to make your own const propagation class (I am not sure - maybe something similar is already provided by boost - please let me know in comments)

My proposition is this class:

#include <memory> // for pointer_traits

template <typename Pointer>
class ConstPropagatePointer 
{
public:
    using element_type = typename std::pointer_traits<Pointer>::element_type;
    using pointer = typename std::pointer_traits<Pointer>::pointer;
    using const_pointer = element_type const * const;
    using reference = element_type&;
    using const_reference = element_type const&;

    ConstPropagatePointer(Pointer ptr) : ptr(ptr) {}
    pointer operator -> ()
    {
        return &(*ptr);
    }
    const_pointer operator -> () const
    {
        return &(*ptr);
    }
    reference operator * ()
    {
        return *ptr;
    }
    const_reference operator * () const 
    {
        return *ptr;
    }
private:
    Pointer ptr;
};

So that will work for you:

class Foo
{
public:
private:
    ConstPropagatedPointer<char*> str; 
    ConstPropagatedPointer<ComplexObj*> obj; 
    ConstPropagatedPointer<std::shared_ptr<ComplexObj>> obj2;
};