Report a compile time error when an class must have a virtual destructor but doesn't have one.

Specifically, the following cases now result in a compile-time error (instead of undefined behavior):
* registerProvider() called with a lambda that returns a pointer to an abstract class with no virtual destructor
* registerMultibindingProvider() called with a lambda that returns a pointer to an abstract class with no virtual destructor
* registerFactory() called with a lambda that returns a std::unique_ptr<T>, with T an abstract class with no virtual destructor
* bind<I, C>() used to bind a std::function<std::unique_ptr<I>(Args...)> to a std::function<std::unique_ptr<C>(Args...)> and I doesn't have a virtual destructor

1 files changed, 2 insertions, 0 deletions

diff --git a/examples/scaling_doubles/scaler.h b/examples/scaling_doubles/scaler.h
index 036b8e6..58fa48c 100644
--- a/examples/scaling_doubles/scaler.h
+++ b/examples/scaling_doubles/scaler.h
@@ -22,6 +22,8 @@
 class Scaler {
 public:
   virtual double scale(double x) = 0;
+
+  virtual ~Scaler() = default;
 };
 
 using ScalerFactory = std::function<std::unique_ptr<Scaler>(double)>;