C#•3y ago•

33 replies

✅ Recursive type definition

This is valid (basically CRTP):

class Base<T> { }
class Derived<T> : Base<Derived<T>> { }

class Base<T> { }
class Derived<T> : Base<Derived<T>> { }

This is not, because if you instantiate anywhere a

new Derived<SomeType>()

new Derived<SomeType>()

, the program panics with

TypeLoaderException

TypeLoaderException

because of "recursive generic definition"

class Base<T> { }
class Derived<T> : Base<Derived<Derived<T>>> { }

class Base<T> { }
class Derived<T> : Base<Derived<Derived<T>>> { }

I cannot understand the different between these two generic definitions.
If I specify

SomeType

SomeType

, I would imagine that the generics should expand as expected and resolve the types correctly, as kind-0 types, e.g.:

Derived<int> : Base<Derived<Derived<int>>>

Derived<int> : Base<Derived<Derived<int>>>

The only thing I could find is the official explanation on the CLI Standard here on page 129 https://www.ecma-international.org/publications-and-standards/standards/ecma-335/, but I do not quite get it.

Any ideas?

Ecma InternationalElisa Denis

Common Language Infrastructure (CLI) - Defines the infrastructure in which applications written in multiple high-level languages can be executed