Getting F-bounded polymorphism into shape

Abstract

We present a way to restrict recursive inheritance without sacrificing the benefits of F-bounded polymorphism. In particular, we distinguish two new concepts, materials and shapes , and demonstrate through a survey of 13.5 million lines of open-source generic-Java code that these two concepts never actually overlap in practice. With this Material-Shape Separation , we prove that even naïve type-checking algorithms are sound and complete, some of which address problems that were unsolvable even under the existing proposals for restricting inheritance. We illustrate how the simplicity of our design reflects the design intuitions employed by programmers and potentially enables new features coming into demand for upcoming programming languages.

Study of the Subtyping Machine of Nominal Subtyping with Variance (full version)

“…Greenman et al [2014] raised a concern about non-expansive inheritance restricting some conventional class table use-cases. We go one step further by showing that the expressiveness of non-expansive class tables is regular, i.e., of the lowest tier.Theorem 5.1.…”