Add optional custom comparator to SetOnce<T, CompareEq>

lib/core/include/qx/core/qx-setonce.h

@@ -4,22 +4,27 @@
 // Standard Library Includes
 #include <type_traits>
 
+// Extra-component Includes
+#include <qx/utility/qx-concepts.h>
+
 namespace Qx
 {
 
-template<typename T>
-    requires std::is_assignable_v<T&, T>
+template<typename T, class CompareEq = std::equal_to<T>>
+    requires std::is_assignable_v<T&, T> && Qx::defines_call_for_s<CompareEq, bool, T, T>
 class SetOnce
 {
 //-Instance Members----------------------------------------------------------------------------------------------------
 private:
+    CompareEq mComparator;
     bool mSet;
     T mDefaultValue;
     T mValue;
 
 //-Constructor-------------------------------------------------------------------------------------------------------
 public:
-    SetOnce(T initial) :
+    SetOnce(T initial, const CompareEq& comp = CompareEq()) :
+        mComparator(comp),
         mSet(false),
         mDefaultValue(initial),
         mValue(initial)
@@ -36,9 +41,9 @@ class SetOnce
         mValue = mDefaultValue;
     }
 
-    SetOnce<T>& operator=(const T& value)
+    SetOnce<T, CompareEq>& operator=(const T& value)
     {
-        if(!mSet && mDefaultValue != value)
+        if(!mSet && !mComparator(mDefaultValue, value))
         {
             mValue = value;
             mSet = true;

lib/core/src/qx-setonce.dox

@@ -9,35 +9,44 @@ namespace Qx
  *  @ingroup qx-core
  *
  *  @brief The SetOnce template class acts as a container for a value that can only be set once.
+ *
+ *  The optional @a CompareEq template parameter can be used to provide a custom compare-equal function
+ *  object type.
  */
 
 //-Constructor----------------------------------------------------------------------------------------------
 //Public:
 /*!
- * @fn SetOnce<T>::SetOnce(T initial)
+ * @fn SetOnce<T, CompareEq>::SetOnce(T initial, const CompareEq& comp)
  *
  *  Creates a SetOnce container that holds the initial value @a initial.
  *
  *  The container is initially unset and only holds this value until it is set.
+ *
+ *  Optionally, a custom compare-equal function can be provided through @a comp, which
+ *  is used to determine whether or not an assigned value is different from the
+ *  container's initial value.
+ *
+ *  @sa operator=(const T& value).
  */
 
 
 //-Instance Functions----------------------------------------------------------------------------------------------
 //Public:
 /*!
- * @fn SetOnce<T>::isSet() const
+ * @fn SetOnce<T, CompareEq>::isSet() const
  *
  *  Returns @c true if the containers value has been set; otherwise returns @c false.
  */
 
 /*!
- * @fn const T& SetOnce<T>::value() const
+ * @fn const T& SetOnce<T, CompareEq>::value() const
  *
  *  Returns the current value of the container.
  */
 
 /*!
- * @fn void SetOnce<T>::reset()
+ * @fn void SetOnce<T, CompareEq>::reset()
  *
  *  Resets the container to its initial state.
  *
@@ -47,7 +56,7 @@ namespace Qx
  */
 
 /*!
- * @fn SetOnce<T>& SetOnce<T>::operator=(const T& value)
+ * @fn SetOnce<T, CompareEq>& SetOnce<T, CompareEq>::operator=(const T& value)
  *
  *  Sets the value of the container to @a value, if it is different from its initial value.
  *