singly rooted hierarchy

The singly rooted hierarchy, in object-oriented programming, is a characteristic of most (but not all) OOP-based programming languages. In most such languages, in fact, all classes inherit directly or indirectly from a single root, usually with a name similar to Object; all classes then form a common inheritance hierarchy.

This idea was introduced first by Smalltalk, and was since used in most other object-oriented languages (notably Java and C#). This feature is especially useful for container libraries - they only need to allow putting an Object in a container to allow objects of any class to be put in the container.

A notable exception is C++, where (mainly for compatibility with C and efficiency) there is no single object hierarchy. Containers in C++ have been implemented with multiple inheritance,Bruce Eckel, Thinking in C++ vol. 2, Ch. 9 "Multiple inheritance": section "Perspective" and with help of template-based generic programming by Bjarne Stroustrup.[http://www.codeguru.com/cpp/tic/tic0246.shtml MFC Programmer's SourceBook : Thinking in C] {{webarchive|url=https://web.archive.org/web/20071113163132/http://www.codeguru.com/cpp/tic/tic0246.shtml |date=2007-11-13 }}Bruce Eckel, Thinking in C++ vol. 1, Ch. 16 "Introduction to Templates": section "The template solution" Other object-oriented languages without a singly rooted hierarchy include Objective-C and PHP.