Affiliations: Dipartimento di Informatica, Università di Torino, C.so Svizzera 185, 1-10149 Torino, Italy. V.Bono@cs.bham.ac.uk | Dipartimento di Matematica, Università di Padova, Via Belzoni 7, 1-35131 Padova, Italy. michele@dsi.unive.it | Dipartimento di Informatica, Università di Torino, C.so Svizzera 185, 1-10149 Torino, Italy. dezani@di.unito.it | Dipartimento di Matematica ed Informatica, Università di Udine, Via delle Scienze 206, 1-33100 Udine, Italy. liquori@ens-lyon.fr
Note: [] Current address: School of Computer Science, The University of Birmingham, Edgbaston, Birmingham B15 2TT, U.K.
Note: [] Current address: Dipartimento di Informatica, Università “Ca' Foscari” di Venezia, via Torino 155, 30123 Mestre, Italy.
Note: [] Partly supported by NATO Grant HTECH.LG960875.
Note: [] Current address: Laboratoire de l'informatique du Parallélisme, Ècole Normale Supérieure de Lyon, F-69364 Lyon, France.
Abstract: We extend the type system for the Lambda Calculus of Objects [16] with a mechanism of width subtyping and a treatment of incomplete objects. The main novelties over previous work are the use of subtype-bounded quantification to capture a new and more direct rendering of MyType polymorphism, and a uniform treatment for other features that were accounted for via different systems in subsequent extensions [7, 6] of [16]. The new system provides for (i) appropriate type specialization of inherited methods, (ii) static detection of errors, (iii) width subtyping compatible with object extension, and (iv) sound typing for partially specified objects.
Keywords: Objects, Type System, Subtyping, Type Soundness
