You can add rules to your setter, to ensure that another class can't set it arbitrarily. Say, for example, an Age field. This should always be greater than (or possibly equal to) zero. You can write your setter to reject any values which aren't. A public Age field could be set by another class to any number it wants to. More on reddit.com

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I am very interested in the mapping. Will you publish it after you have finished your work? Which concepts do you take as essential for oo? I have used this paper in the past Armstrong 2006: The Quarks of Object-oriented Development For essential functional concepts is use Janecek 2017: Analysing Functional Paradigm Concepts More on reddit.com

class Foo { public: int length(); private: int begin; int end; }; begin and end are encapsulated. class Bar : public Foo { public: int min(); int max(); }; Bar inherits from Foo. int squareLength(Foo& foo) { int length = foo.length(); return length*length; } Bar bar; int baz = squareLength(bar); bar is passed to squareLength polymorphic. More on reddit.com