STYLE: SingletonIndex does not need to store the unused func parameter

No longer stored the `func` parameter from `SingletonIndex::SetGlobalInstance`,
as it was never actually retrieved afterwards.

Deprecated the `SingletonIndex::SingletonData` type alias, as it is no longer
used internally anymore, and it should not be public either.

Modules/Core/Common/include/itkSingleton.h

@@ -47,7 +47,12 @@ class ITKCommon_EXPORT SingletonIndex
 public:
   /** Standard class types. */
   using Self = SingletonIndex;
-  using SingletonData = std::map<std::string, std::tuple<void *, std::function<void(void *)>, std::function<void()>>>;
+
+#ifndef ITK_LEGACY_REMOVE
+  using SingletonData [[deprecated("The internal representation of the singleton data is private, and may not "
+                                   "correspond with SingletonData anymore.")]] =
+    std::map<std::string, std::tuple<void *, std::function<void(void *)>, std::function<void()>>>;
+#endif
 
   // obtain a global registered in the singleton index under the
   // globalName, if unknown then nullptr will be returned.
@@ -67,10 +72,10 @@ class ITKCommon_EXPORT SingletonIndex
   bool
   SetGlobalInstance(const char *                globalName,
                     T *                         global,
-                    std::function<void(void *)> func,
+                    std::function<void(void *)> itkNotUsed(func),
                     std::function<void()>       deleteFunc)
   {
-    return this->SetGlobalInstancePrivate(globalName, global, func, deleteFunc);
+    return this->SetGlobalInstancePrivate(globalName, global, deleteFunc);
   }
 
   /** Set/Get the pointer to GlobalSingleton.
@@ -93,17 +98,14 @@ class ITKCommon_EXPORT SingletonIndex
   // If globalName is already registered than false is return,
   // otherwise global is added to the singleton index under globalName
   bool
-  SetGlobalInstancePrivate(const char *                globalName,
-                           void *                      global,
-                           std::function<void(void *)> func,
-                           std::function<void()>       deleteFunc);
+  SetGlobalInstancePrivate(const char * globalName, void * global, std::function<void()> deleteFunc);
 
   /** The static GlobalSingleton. This is initialized to nullptr as the first
    * stage of static initialization. It is then populated on the first call to
    * itk::Singleton::Modified() but it can be overridden with SetGlobalSingleton().
    * */
-  SingletonData m_GlobalObjects;
-  static Self * m_Instance;
+  std::map<std::string, std::tuple<void *, std::function<void()>>> m_GlobalObjects;
+  static Self *                                                    m_Instance;
   //  static SingletonIndexPrivate * m_GlobalSingleton;
 };
 

Modules/Core/Common/src/itkSingleton.cxx

@@ -87,8 +87,7 @@ namespace itk
 void *
 SingletonIndex::GetGlobalInstancePrivate(const char * globalName)
 {
-  SingletonData::iterator it;
-  it = m_GlobalObjects.find(globalName);
+  const auto it = m_GlobalObjects.find(globalName);
   if (it == m_GlobalObjects.end())
   {
     return nullptr;
@@ -99,13 +98,10 @@ SingletonIndex::GetGlobalInstancePrivate(const char * globalName)
 // If globalName is already registered remove it from map,
 // otherwise global is added to the singleton index under globalName
 bool
-SingletonIndex::SetGlobalInstancePrivate(const char *                globalName,
-                                         void *                      global,
-                                         std::function<void(void *)> func,
-                                         std::function<void()>       deleteFunc)
+SingletonIndex::SetGlobalInstancePrivate(const char * globalName, void * global, std::function<void()> deleteFunc)
 {
   m_GlobalObjects.erase(globalName);
-  m_GlobalObjects.insert(std::make_pair(globalName, std::make_tuple(global, func, deleteFunc)));
+  m_GlobalObjects.insert(std::make_pair(globalName, std::make_tuple(global, deleteFunc)));
   return true;
 }
 
@@ -130,7 +126,7 @@ SingletonIndex::~SingletonIndex()
 {
   for (auto & pair : m_GlobalObjects)
   {
-    std::get<2>(pair.second)();
+    std::get<1>(pair.second)();
   }
 }