A formal definition of subtyping
in the Julia language,
a dynamic language for scientific computing with multiple symmetric dispatch,
user-defined parametric types, union types, and existential types.
In Julia, subtyping is used at run time, for multiple-dispatch resolution.
Julia Subtyping: A Rational ReconstructionAuthors: Francesco Zappa Nardelli, Julia Belyakova, Artem Pelenitsyn, Benjamin Chung, Jeff Bezanson, Jan Vitek
Venue: Proc. ACM Program. Lang., Volume 2, OOPSLA, Article 113 (28 pages)
Programming languages that support multiple dispatch rely on an expressive notion of subtyping to specify method applicability. In these languages, type annotations on method declarations are used to select, out of a potentially large set of methods, the one that is most appropriate for a particular tuple of arguments. Julia is a language for scientific computing built around multiple dispatch and an expressive subtyping relation. This paper provides the first formal definition of Julia's subtype relation and motivates its design. We validate our specification empirically with an implementation of our definition that we compare against the existing Julia implementation on a collection of real-world programs. Our subtype implementation differs on 122 subtype tests out of 6014476. The first 120 differences are due to a bug in Julia that was fixed once reported; the remaining 2 are under discussion.