Subtype polymorphism

[jasper310899]

As part of my bachelorthesis I worked on exending Autocxx's support for polymorphism, specifically subtype polymorphism.

This allows non-virtual methods to be called on child class objects as well as using child class references as baseclass refernce parameters values.

Currently only 75% of the tests are passing so I wanted to get an image of if you think this is worth fixing up.

The way I implemented it was as post processing after the last step before codegen:
Methods get implemented on a extension trait which is implemented for all childclasses.
Furthermore functions with reference parameters get wrapped in a function that takes a impl-type parameter.

This process is currently disabled for virtual functions with reference parameters.

For examples of what this allows please check out: https://git.yasupa.de/jasper3108/BA-2/src/branch/master/Abgabe/ch7/src/main.rs and https://git.yasupa.de/jasper3108/BA-2/src/branch/master/Abgabe/ch7/src/header.hpp for the C++ code.

My CLA is already applied but im still waiting for it.

Jasper W.

[jasper310899]

I should also add that the traitbound used for polymorphis automatically detects anything that can be derefenced into a childcass.

This allows doing things like bindings::call_inherit_me(&bindings::B::new().within_box()); or moveit! { let mut obj = bindings::B::new() }; assert_eq!(bindings::call_mut(&mut obj).0, 42); while not breaking backwards compability.

[adetaylor]

Thanks for raising this!

I'm definitely interested in getting this to a place where it can be merged.

The main things missing from this PR are:

• integration tests
• docs (in book/ and the APIs)
• probably an example too

Once it's a bit more complete (and tests all pass) I'll go through and do a review.