Proceedings of the 23rd Annual ACM SIGPLAN Conference on Object-Oriented Programming, Systems, Languages, and Applications, OOPSLA 2008 pages:423-438
OOPSLA edition:23 location:Nashville, Tennessee, USA date:19-23 October 2008
With Java 5 and C# 2.0, first-order parametric polymorphism was introduced in mainstream object-oriented programming languages under the name of generics. Although the first-order variant of generics is very useful, it also imposes some restrictions: it is possible to abstract over a type, but the resulting type constructor cannot be abstracted over. This can lead to code duplication. We removed this restriction in Scala, by allowing type constructors as type parameters and abstract type members. This paper presents the design and implementation of the resulting type constructor polymorphism. Furthermore, we study how this feature interacts with existing object-oriented constructs, and show how it makes the language more expressive.