After removing the interface, inversion of control, and protected access capabilities from traditional inheritance, what do we have left (besides composition)? This is what we have: placing a few extra tokens on a derived class causes all named fields and methods of one or more base classes to be absorbed as if explicitly incorporated. Further, certain inherited methods can be customized (overridden) with their own implementation. The primary selling point for inheritance has always been this sort of code reuse.
Having spoken about the compiler’s IR tree in general terms, let’s focus in on an important detail: how to represent a node that could be any arbitary type. Cone’s IR makes use of dozens of different types of nodes, each defined using a different struct. However, sometimes the compiler needs to point to a node without restricting which type of node it must be. For example, consider an assignment node.