DenseStorage safely copy/swap.

Fixes #2229.

For dynamic matrices with fixed-sized storage, only copy/swap
elements that have been set.  Otherwise, this leads to inefficient
copying, and potential UB for non-initialized elements.

test/rvalue_types.cpp

@@ -13,41 +13,12 @@
 #if EIGEN_HAS_CXX11
 #include "MovableScalar.h"
 #endif
+#include "SafeScalar.h"
 
 #include <Eigen/Core>
 
 using internal::UIntPtr;
 
-// A Scalar that asserts for uninitialized access.
-template<typename T>
-class SafeScalar {
- public:
-  SafeScalar() : initialized_(false) {}
-  SafeScalar(const SafeScalar& other) {
-    *this = other;
-  }
-  SafeScalar& operator=(const SafeScalar& other) {
-    val_ = T(other);
-    initialized_ = true;
-    return *this;
-  }
-  
-  SafeScalar(T val) : val_(val), initialized_(true) {}
-  SafeScalar& operator=(T val) {
-    val_ = val;
-    initialized_ = true;
-  }
-  
-  operator T() const {
-    VERIFY(initialized_ && "Uninitialized access.");
-    return val_;
-  }
- 
- private:
-  T val_;
-  bool initialized_;
-};
-
 #if EIGEN_HAS_RVALUE_REFERENCES
 template <typename MatrixType>
 void rvalue_copyassign(const MatrixType& m)