Constructor Rules: Class Must Have Exactly One Primary Constructor

In the article about first constructor rule, we’ve seen that classes must have at least one constructor, otherwise they are reduced to a sorry imitation of what they should be. We also concluded that the first constructor in a class must validate the parameters and just assign them to the fields and do nothing else. Here we’ll cover the next rule: why such constructors deserve to be called primary constructors and why classes must have exactly one of them.