BUG: Fix linking by making LBFGS2Optimizerv4 a template

Having LGBFGS2 being a compiled class in the Optimizerv4 library
created linking errors from duplicate symbols on Windows with shared
libraries in certain situations. The cause is that the parent classes
of LBGFS2 were templated, and their link specifcation is not
compatibile for them being in a shared library.

The implemented solution was to make the LBFGS2 Optimizer a template
class like its parents so that its symbols will not be in a shared
library.

Author: blowekamp

Modules/Numerics/Optimizersv4/include/itkLBFGS2Optimizerv4.h

@@ -25,7 +25,7 @@
 namespace itk
 {
 /*** \class LBFGS2Optimizerv4Enums
- * \brief Scoped Enum classes for LBFGS2Optimizerv4 class
+ * \brief Scoped Enum classes for LBFGS2Optimizerv4Template class
  * \ingroup ITKOptimizersv4
  */
 class LBFGS2Optimizerv4Enums
@@ -82,7 +82,7 @@ extern ITKOptimizersv4_EXPORT std::ostream &
                               operator<<(std::ostream & out, LBFGS2Optimizerv4Enums::LineSearchMethod value);
 
 /**
- *\class LBFGS2Optimizerv4
+ *\class LBFGS2Optimizerv4Template
  * \brief Wrap of the libLBFGS[1] algorithm for use in ITKv4 registration framework.
  * LibLBFGS is a translation of LBFGS code by Nocedal [2] and adds the orthantwise
  * limited-memmory Quais-Newton method [3] for optimization with L1-norm on the
@@ -153,11 +153,13 @@ extern ITKOptimizersv4_EXPORT std::ostream &
  *
  * \ingroup ITKOptimizersv4
  */
-class ITKOptimizersv4_EXPORT LBFGS2Optimizerv4 : public GradientDescentOptimizerv4Template<double>
+template <typename TInternalComputationValueType>
+class ITK_TEMPLATE_EXPORT LBFGS2Optimizerv4Template
+  : public GradientDescentOptimizerv4Template<TInternalComputationValueType>
 {
 
 public:
-  ITK_DISALLOW_COPY_AND_MOVE(LBFGS2Optimizerv4);
+  ITK_DISALLOW_COPY_AND_MOVE(LBFGS2Optimizerv4Template);
 
   using LineSearchMethodEnum = LBFGS2Optimizerv4Enums::LineSearchMethod;
 #if !defined(ITK_LEGACY_REMOVE)
@@ -181,14 +183,14 @@ class ITKOptimizersv4_EXPORT LBFGS2Optimizerv4 : public GradientDescentOptimizer
   using PrecisionType = double;
 
   /** Standard "Self" type alias. */
-  using Self = LBFGS2Optimizerv4;
-  using Superclass = GradientDescentOptimizerv4Template<double>;
+  using Self = LBFGS2Optimizerv4Template;
+  using Superclass = GradientDescentOptimizerv4Template<TInternalComputationValueType>;
   using Pointer = SmartPointer<Self>;
   using ConstPointer = SmartPointer<const Self>;
 
-  using MetricType = Superclass::MetricType;
-  using ParametersType = Superclass::ParametersType;
-  using ScalesType = Superclass::ScalesType;
+  using MetricType = typename Superclass::MetricType;
+  using ParametersType = typename Superclass::ParametersType;
+  using ScalesType = typename Superclass::ScalesType;
 
   /** Stop condition return string type */
   using typename Superclass::StopConditionReturnStringType;
@@ -197,7 +199,7 @@ class ITKOptimizersv4_EXPORT LBFGS2Optimizerv4 : public GradientDescentOptimizer
   itkNewMacro(Self);
 
   /** Run-time type information (and related methods). */
-  itkTypeMacro(LBFGS2Optimizerv4, GradientDescentOptimizerv4Template);
+  itkTypeMacro(LBFGS2Optimizerv4Template, GradientDescentOptimizerv4Template);
 
   /** Start optimization with an initial value. */
   void
@@ -457,8 +459,8 @@ class ITKOptimizersv4_EXPORT LBFGS2Optimizerv4 : public GradientDescentOptimizer
   itkBooleanMacro(EstimateScalesAtEachIteration);
 
 protected:
-  LBFGS2Optimizerv4();
-  ~LBFGS2Optimizerv4() override;
+  LBFGS2Optimizerv4Template();
+  ~LBFGS2Optimizerv4Template() override;
   void
   PrintSelf(std::ostream & os, Indent indent) const override;
 
@@ -534,8 +536,18 @@ class ITKOptimizersv4_EXPORT LBFGS2Optimizerv4 : public GradientDescentOptimizer
   void
   AdvanceOneStep() override
   {
-    itkWarningMacro("LBFGS2Optimizerv4 does not implemenetd single step advance");
+    itkWarningMacro("LBFGS2Optimizerv4Template does not implemenetd single step advance");
   };
 };
+
+
+/** This helps to meet backward compatibility */
+using LBFGS2Optimizerv4 = LBFGS2Optimizerv4Template<double>;
+
 } // end namespace itk
+
+#ifndef ITK_MANUAL_INSTANTIATION
+#  include "itkLBFGS2Optimizerv4.hxx"
+#endif
+
 #endif