Singly rooted hierarchy

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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#).

A notable exception is C++, where (mainly for compatibility with C and efficiency) there is no single object hierarchy. 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. Containers in C++ have been implemented with multiple inheritance,[1] and with help of template-based generic programming by Bjarne Stroustrup.[2][3] Other object-oriented languages without a singly rooted hierarchy include Objective-C and PHP.

See also[edit]


  1. ^ Bruce Eckel, Thinking in C++ vol. 2, Ch. 9 "Multiple inheritance": section "Perspective"
  2. ^ MFC Programmer's SourceBook : Thinking in C
  3. ^ Bruce Eckel, Thinking in C++ vol. 1, Ch. 16 "Introduction to Templates": section "The template solution"