Beware inheritance over composition

Whenever there is inheritance in an object-oriented design ask yourself two questions: 1) Am I a special type of the thing I'm inheriting from? and 2) Is the thing I'm inheriting from part of me? -- Riel's Heuristic 6.2, Arthur Riel 1996

Explanation

Riel believes that inheritance should be treated with care. Before using it, the design decision should be questioned. Does it make sense for this class to be a subclass of another, is the class actually a generalised type of me?

See also

• Riel's heuristics
• Favor composition over inheritance
• Multiple Inheritance
• Avoid multiple inheritance