C# - 扩展泛型参数的泛型接口

Question

Is it possible to define a generic interface that extends the interface's generic parameter?

Eg (this doesn't compile since inheriting T is not possible)

public interface IInsecurableService<T>: T { }

This way I'd like to add services to a DI container that are capable of some functions, while the same service without the extensions does still exists / can still be registered.

Answer 1

ECMA-335 , which defines the CLR, explicitly excludes this scenario , and gives a rationale (section §9.1, my bold):

A generic parameter, on its own, cannot be used to specify the base class, or any implemented interfaces. So, for example, .class ... G``1<T> extends !0 is invalid. However, it is valid for the base class, or interfaces, to use that generic parameter when nested within another generic type. For example, .class ... G``1<T> extends class H``1<!0> and .class ... G``1<T> extends class B``2<!0,int32> are valid.

[ Rationale: This permits checking that generic types are valid at definition time rather than at instantiation time. eg, in .class ... G``1<T> extends !0 , we do not know what methods would override what others because no information is available about the base class; indeed, we do not even know whether T is a class: it might be an array or an interface. Similarly, for .class ... C``2<(!1)T,U> where we are in the same situation of knowing nothing about the base class/interface definition. end rationale ]

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ECMA-334 , which defines the C# language spec, also excludes it (section §18.2.4):

The explicit base interfaces can be constructed interface types (§9.4, §18.2). A base interface cannot be a type parameter on its own, though it can involve the type parameters that are in scope.

Also section §15.2.4.2

The base class specified in a class declaration can be a constructed class type (§9.4). A base class cannot be a type parameter on its own (§9.5), though it can involve the type parameters that are in scope.