[boost] safe_dereference()

From: Anthony Williams (anthwil_at_[hidden])
Date: 2002-09-04 03:36:52

David B. Held writes:
 > I just wrote this little utility function, and wondered if it is generally
 > useful.
 > 
 >     // Requirements:
 >     //   Ptr must define element_type
 >     //   Ptr::element_type must be default-constructible
 >     template <class Ptr>
 >     typename Ptr::element_type const& safe_dereference(Ptr p)
 >     {
 >         return p ? *p : typename Ptr::element_type();
 >     }
 > 
 >     // Requirements:
 >     //   T must be default-constructible
 >     template <typename T>
 >     T const& safe_dereference(T* p)
 >     {
 >         return p ? *p : T();
 >     }
 > 
 > In my use case, I am storing shared_ptrs which may or may not actually
 > point to something.  I want to be able to dereference it regardless, and
 > just get a default value when the pointer is null (which should be obvious
 > enough from the code).  

I can see the point, but this is undefined behaviour --- you are returning a
reference to a temporary, which as gone out of scope.

Anthony