A set function (or setter) is an object mutator. You use it to modify a property of an object such that the object's invariant is maintained. If the object has no invariant, a setter is not required.

A get function (or getter) is an object accessor. You use it to obtain a property from an object such that the object's invariant is maintained. If the object has no invariant, you do not need a getter.

A Zeuthen-Segre invariant is an invariant of complex projective surfaces.

C++ has no notion of concepts, but it has the ability to express ideas in code. For instance, if a variable must be non-zero, that idea can be expressed in code via a class invariant. The constructors ensure the variable is non-zero (throwing an exception when the invariant does not hold). Upon entry to any instance member function that modifies the variable (mutators or setters), you already know the invariant holds true (otherwise the instance would not exist), you simply have to ensure the invariant still holds true before those functions return. Thus the entire idea is encapsulated by the class itself. If a class must contain several invariants, it often makes sense to create one class per invariant, then use composition to combine those invariants into a single class.

yes

Andrzej Pelc has written:

'Invariant measures and ideals on discrete groups' -- subject(s): Discrete groups, Ideals (Algebra), Invariant measures