C++ Programming/Law of three

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The "law of three" in C++ programming is not really a law, but rather a guideline: if a class needs an explicitly declared copy constructor, copy assignment operator, or destructor, then it usually needs all three.

There are exceptions to this rule (or, to look at it another way, refinements). For example, sometimes a destructor is explicitly declared just in order to make it virtual; in that case there's not necessarily a need to declare or implement the copy constructor and copy assignment operator.

Most classes should not declare any of the "big three" operations; classes that manage resources generally need all three..