Ownership questions

[osrf-migration]

Original report (archived issue) by Louise Poubel (Bitbucket: chapulina, GitHub: chapulina).

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I noticed on the examples that it is common to use Scene::Create* functions to instantiate most of the rendering types, as opposed to directly calling the type's constructor. All Create* functions return shared pointers.

1. Does the scene keep shared ownership of everything which is created by Scene::Create*?

This seems to be true for some types but not others, for example:

    auto light = scene->CreateDirectionalLight();
    ASSERT_EQ(light.use_count(), 2u); // passes

    auto ray = scene->CreateRayQuery();
    ASSERT_EQ(ray.use_count(), 1u); // passes

I'd suggest we return `unique_ptr`s for those which the scene won't be keeping1. When calling `Visual::AddChild`, is the ownership shared with the visual? The same goes for other `Add` and `Set` functions which take `shared_ptr`s

1. What's the appropriate way to destroy something which was created with Scene::Create*? There are some Scene::Destroy* functions, but there isn't a 1-1 relation to the creates. How to destroy the missing ones?

2. Is there a situation when an object should / could be instantiated without the use of Scene::Create*?

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

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• Edited issue description

[osrf-migration]

Original comment by Nate Koenig (Bitbucket: Nathan Koenig).

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• Edited issue description