Static Type Inference for Ruby

Many general-purpose, object-oriented scripting languages are dynamically typed, which provides flexibility but leaves the programmer without the benefits of static typing, including early error detection and the documentation provided by type annotations. This paper describes Diamondback Ruby (DRuby), a tool that blends Ruby's dynamic type system with a static typing discipline. DRuby provides a type language that is rich enough to precisely type Ruby code the authors have encountered, without unneeded complexity. When possible, DRuby infers static types to discover type errors in Ruby programs.