Ruby 3.0.0 Preview 1 Released

RBS is a language to describe the types of Ruby programs. Type checkers including type-profiler and other tools supporting RBS will understand Ruby programs much better with RBS definitions.You can write down the definition of classes and modules: methods defined in the class, instance variables and their types, and inheritance/mix-in relations. The goal of RBS is to support commonly seen patterns in Ruby programs and it allows writing advanced types including union types, method overloading, and generics. It also supports duck typing with interface types.Ruby 3.0 ships with rbs gem, which allows parsing and processing type definitions written in RBS.The following is a small example of RBS.