References aren't nullable in ISO C++

[psygate]

Issue:

The documentation in mesh.h maybe wrong, or the documentation is correct and the chosen type (MatrixX&, Reference Type) is wrong. References can't be null by the C++ standard, and if they are this may lead to undefined behaviour.

See https://en.cppreference.com/w/cpp/language/reference_initialization and https://en.cppreference.com/w/cpp/language/reference

How to reproduce the bug:

`

	const auto m_N(lRec.mesh->getVertexNormals());

	std::cout << m_N(0) << std::endl;

	return { 0.0f };

`

This crashes with an AccessViolationException@NULL, which can't or shouldn't happen with references, since they can't be null.

Solution:

Change the reference to a ptr type (MatrixX*) or change the MatrixX to be an empty matrix and provide a function to check whether normals exist (bool hasVertexNormals() for instance).

[peacememories]

Are you sure that is what's happening? I tried the code you provided (in my instance inside AmbientOcclusionIntegrator->Li) and sure enough i got access violations. But those do not stem from m_N directly, which is not, in fact, a nullptr but a perfectly valid instance of MatrixXf. ( cout << &m_N; results in non-null addresses being printed)

What is happening is that those instances are of length 0. Check m_N.size(), which should return 0. Since you are accessing a member of a zero-size matrix, you are running into access violations.

I'm assuming that the documentation is wrong, and is an artifact of the signature being switched from pointer returns to references at some point, although the git history does not seem to show this.