ADT design (1)
A constructor is an operation that creates a value of the ADT (dans une classe qui implante cet ADT)
An accessor is an operation that uses a value of the ADT to compute a value of some other type.
A transformer is an operation that computes a new value of the same ADT.
A well-designed ADT provides at least one constructor, at least one accessor, and at least one transformer. The constructors and transformers together can generate all values of the ADT.