Move methods to NexusFileLoader

Framework/API/inc/MantidAPI/IFileLoader.h

@@ -24,7 +24,6 @@ public:
   /// Returns a value indicating whether or not loader wants to load multiple
   /// files into a single workspace
   virtual bool loadMutipleAsOne() { return false; }
-  virtual void execLoader() {}
 };
 
 } // namespace API

Framework/DataHandling/inc/MantidDataHandling/NexusFileLoader.h

@@ -15,7 +15,8 @@ namespace Mantid::DataHandling {
 class DLLExport NexusFileLoader
     : public API::IFileLoader<Mantid::Kernel::NexusHDF5Descriptor> {
 public:
-  void exec() override;
+  void exec() override final;  // makes sure the NexusHDF5Descriptor is initialized
+  virtual void execLoader() = 0;  // what would normally be called exec
   boost::shared_ptr<Algorithm> createChildAlgorithm(
       const std::string &name, const double startProgress = -1.,
       const double endProgress = -1., const bool enableLogging = true,

Framework/DataHandling/src/NexusFileLoader.cpp

@@ -7,16 +7,24 @@
 #include "MantidDataHandling/NexusFileLoader.h"
 
 namespace Mantid::DataHandling {
-void NexusFileLoader::exec() { execLoader(); }
+void NexusFileLoader::exec() {
+  // make sure the descriptor is initialized
+  if (!m_fileInfo) {
+    const std::string filename = this->getPropertyValue("Filename"); // TODO be more generic
+    m_fileInfo = std::make_shared<Mantid::Kernel::NexusHDF5Descriptor>(filename);
+  }
+
+  // execute the algorithm as normal
+  execLoader();
+}
 boost::shared_ptr<Mantid::API::Algorithm> NexusFileLoader::createChildAlgorithm(
     const std::string &name, const double startProgress,
     const double endProgress, const bool enableLogging, const int &version) {
-  auto child = API::IFileLoader<
-      Mantid::Kernel::NexusHDF5Descriptor>::createChildAlgorithm(name,
-                                                                 startProgress,
-                                                                 endProgress,
-                                                                 enableLogging,
-                                                                 version);
+  auto child = IFileLoader::createChildAlgorithm(name,
+                                                 startProgress, endProgress,
+                                                 enableLogging, version);
+
+  // set the NexusHDF5Descriptor on the child algorithm
   auto nfl = boost::dynamic_pointer_cast<NexusFileLoader>(child);
   if (nfl) {
     nfl->setFileInfo(m_fileInfo);