Здравствуйте, kochetkov.vladimir, Вы писали:

В C# действуют следующие правила:

10.1.4 Class base specification
A base class cannot be a type parameter on its own, though it can involve the type parameters that are in scope.

class Extend<V>: V {}            // Error, type parameter used as base class

10.1.5 Type parameter constraints
In either case, the constraint can involve any of the type parameters of the associated type or method declaration as part of a constructed type, and can involve the type being declared.