Rough implementation to find a concrete list type from an interface

gistfile1.vb

Sub Main
	Dim type = GetType(List(Of String))
	FindExplicitListType(type).Dump()
End Sub

Function FindExplicitListType(type As Type) As Type
	If type.IsClass Then
		'TODO: Should check if type implements IList or IList(Of)
		Return type
	ElseIf IsGenericList(type)
		Return GetExplicitListType(type)
	Else
		Dim found = type.GetInterfaces().Where(AddressOf IsGenericList).ToList()
		If found.Count <> 1
			'TODO: Some sort of error
		End If
		Return GetExplicitListType(found(0))
	End If
	'TODO: Should check if it implements more than one list type
	'TODO: Should check if it implements IList
	'TODO: Should check if it is an array
End Function

Function IsGenericList(type As Type) As Boolean
	Return type.IsGenericType() AndAlso GetType(IList(Of)) Is type.GetGenericTypeDefinition()
End Function

Function GetExplicitListType(type As Type) As Type
	'Assumes IsGenericList(type) returns true
	Dim elementType = type.GetGenericArguments()(0)
	Return GetType(List(Of)).MakeGenericType(elementType)
End Function