A method of reducing the size of compiled and executable computer programs which are edited with the aid of object-oriented programming techniques. The common portions of a program produced by an object-oriented programming technique are separated as untyped implementation classes from the typed interface classes with parameterized templates where the typed interface classes comprise no virtual functions. Untyped implementation classes are arranged in a second polymorph class hierarchy, and method calls to the interface classes are delegated to the implementation classes. The invention is particularly applicable to the technical field of producing class libraries for an object-oriented programming language. The invention advantageously achieves an effective and significant reduction in the size of computer programs and thus allows the computer program to be stored and executed with less demand on the hardware requirements of the computer system.