The earliest one I know of is in the Emerald programming language. There is a brief description of the technique in http://www.emeraldprogramminglanguage.org/OO

The earliest one I know of is in the Emerald programming language. There is a brief description of the technique in http://www.emeraldprogramminglanguage.org/OOPSLA-86-paper.pdf http://www.emeraldprogramminglanguage.org/OOPSLA-86-paper.pd... from 1986. See http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.103.9395&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.103... for more history and description of the implementation. From that paper: "The run-time system constructed an AbCon for each <type, implementation> pair that it encountered. An object reference consisted not of a single pointer, but of a pair of pointers: a pointer to the object itself, and a pointer to the appropriate AbCon". (Called an AbCon because it "mapped Abstract operations to Concrete implementations.)