Ownership, uniqueness and immutability

Abstract. Programming in an object-oriented language demands a fine balance between flexibility and control. At one level, objects need to interact freely to achieve our implementation goals. At a higher level, architectural constraints that ensure the system can be understood by new developers and can evolve as requirements change must be met. To resolve this tension, researchers have developed type systems express-ing ownership and behavioural restrictions such as immutability. This work reports on our consolidation of the resulting discoveries into a sin-gle programming language. Our language, Joe3, imposes little additional syntactic overhead, yet can encode powerful patterns such as fractional permissions and the reference modes of Flexible Alias Protection.