Why are interfaces not strongly typed?
interface, strong-typing, vb.net
Solution
Use `Option Strict On` at the top of your source code file to catch problems like this. You'll get a compile time error instead of a runtime error:
error BC30512: Option Strict On disallows implicit conversions from 'ClassA' to 'IDoThingsC'.
Problem
I have the following code compiles without issue. Of course, I get an invalid cast exception when executing the `Dim C As IDoThingsC = GetThing_C()`. Am I missing something? Would you ever want to return an object that does not meet the interface requirement for a function return value? ``` Public Class ClassA Public Sub DoThings_A() Debug.Print("Doing A things...") End Sub End Class Public Class ClassB Implements IDoThingsC Public Sub DoThings_B() Debug.Print("Doing B things...") End Sub Public Sub DoThings_C() Implements IDoThingsC.DoThings_C Debug.Print("Doing C things...") End Sub End Class Public Interface IDoThingsC Sub DoThings_C() End Interface Public Class aTest Public Sub Test() Dim C As IDoThingsC = GetThing_C() C.DoThings_C() End Sub Public Function GetThing_C() As IDoThingsC Dim Thing As ClassA = New ClassA Thing.DoThings_A() Return Thing End Function End Class ```