public override T GetExtension<T>()
where T : class, IExtension

Public Overrides Function GetExtension(Of T As {Class, IExtension}) As T

public:
generic<typename T>
where T : ref class, IExtension
virtual T GetExtension() override

abstract GetExtension : unit -> 'T  when 'T : not struct and IExtension
override GetExtension : unit -> 'T  when 'T : not struct and IExtension