[phobos] What does this code do?

[David Simcha]

I'm trying to revamp array() to follow Bearophile's very good suggestion 
of letting any foreachable object be convertible to an array even if 
it's opApply-based, not a range.  My efforts have been blocked by this 
cryptic piece of code:

         foreach (ref e; result)
         {
             // hacky
             static if (is(typeof(&e.opAssign)))
             {
                 // this should be in-place construction
                 new(&e) E(r.front);
             }
             else
             {
                 e = r.front;
             }
             r.popFront;
         }

It took me awhile to even wrap my head around what the point of that 
code is.  First of all, why are we bypassing opAssign?  Secondly, what 
if the E doesn't have a constructor that takes only another E as an 
argument?