The general rule: non-leaf classes should be abstract. This will yields dividends in the form of increased reliability, robustness, comprehensibility, and extensibility throughout our software.

Things change. Future tense thinking increases the reusability of the code we write, enhances its maintainability, makes it more robust, and facilitates gracefully in an environment where change is a certainty.

A virtual function call is termed a “message dispatch.” A call that acts virtual on multiple parameters is called multiple dispatch, which is not directly supported in C++. Several resolutions exist, but none is without its disadvantages.

Objects that stand for other objects are often called proxy objects (or surrogates), and the classes that give rise to proxy objects are often called proxy classes, which is useful for implementing multidimensional arrays, differentiating lvalue/rvalue, and suppressing implicit conversions.

Reference counting is technique that allows multiple objects with the same value to share a sinple representation of that value.