Initialize shared_ptr passed by member function parameter

Question

I hope someone can help me how to deal with this situation. Here the issue. I have a shared library (.so, .dll, .dynlib). Within that library there is some sort of factory class that creates objects. For example my method looked like this:

class RenderSystem {
    public:
        int createTexture(Texture** texture, ...);
        ....
}

The createTexture method in the RenderSystem class looks like this:

int createTexture(Texture** texture, ...) {
    ....
    *texture = new ...
    return someErrorCode;
}

It was creating the Texture instance and passing the pointer to the texture parameter. We know that the instances created within a shared library has to be destroyed in the same. So I had methods that was deleting/destroying those textures.

I like to use shared_ptr for all this but I have to keep the return value as integer. What is the correct way return a std::shared_ptr<Texture> without changing the return type of the method. Is it safe to pass a reference to a std::shared_ptr<Texture> or do I have to change the return value of the method into std::shared_ptr<Texutre> ? So is it OK to do this:

int createTexture(std::shared_ptr<Texture>& texture, ...) {
    ....
    texture = std::shared_ptr<....>(...) or std::make_shared<...>(..);
    return someErrorCode;
}

Hope I could describe the problem.

Answer 1

Is it safe to pass a reference...?

Yes, it is not uncommon to use the technique you describe, it is often known as return by reference (or call-by-reference ).

With some systems and conventions, the return by reference arguments are at the end of the method signature - but this is a preference and makes little difference.

... or do I have to change the return value of the method...?

Alternatives that require a change in the return type are:

• Expanding the return type to be a std::tuple or std::pair of some sort.

• Possibly the best would be to return the std::shared_ptr and throw an exception on the error condition.

The alternatives would require a change in the return type, this is not exactly what you asked for, but alternatives worth mentioning.