How to feed a shared_ptr to a template function that shall add various data types to a vector?

Question

In this question it was suggested to use std::shared_ptr instead of std::unique_ptr. However I am not able to make this work when feeding this shared pointer to my function:

 std::vector<std::unique_ptr<segment>> v3;

    //VERSION 5:
    auto myLine2 = std::make_shared<Line>(start, end);
    add_segment(v3, myLine2);

Here's the new implementation of the function:

template<typename T1, typename T2>
inline void add_segment(T1 & v, T2& line_or_circle)
{
    v.emplace_back(std::move(line_or_circle));
}

What am I doing wrong here?

Answer 1

You can't "move" the thing inside a shared_ptr into an instance of a unique_ptr. If you could, all kinds of problems would occur as a result of two different smart pointers trying to delete the thing inside it when they get released.

Instead, just delcare your vector as :

std::vector<std::shared_ptr<segment>> v3;

And then, you really don't need move semantics after that:

template<typename T1, typename T2>
inline void add_segment(T1 & v, T2& line_or_circle)
{
    v.emplace_back(line_or_circle);
}