Add settings object API

Documentation is in `docs/specs/Settings-Object-API.md`.

src/settings/internal/settings_object_data.h

@@ -0,0 +1,75 @@
+#pragma once
+#include <list>
+#include <easylogging++.h>
+
+namespace settings
+{
+class SettingsObjectData
+{
+public:
+    template <typename Value> void addValue( const Value value )
+    {
+        std::list<Value>& list = getListObject<Value>();
+
+        list.push_back( value );
+    }
+
+    template <typename Value>
+    Value getNextValueOrDefault( const Value defaultValue )
+    {
+        Value returnedValue = defaultValue;
+
+        std::list<Value>& list = getListObject<Value>();
+
+        if ( hasValuesOfType<Value>() )
+        {
+            returnedValue = list.front();
+            list.pop_front();
+        }
+
+        return returnedValue;
+    }
+
+    template <typename Value> bool hasValuesOfType()
+    {
+        std::list<Value>& list = getListObject<Value>();
+
+        return !list.empty();
+    }
+
+private:
+    template <typename Value> std::list<Value>& getListObject()
+    {
+        using std::is_same;
+        const auto isBool = is_same<bool, Value>::value;
+        const auto isInt = is_same<int, Value>::value;
+        const auto isDouble = is_same<double, Value>::value;
+        const auto isString = is_same<std::string, Value>::value;
+
+        static_assert( isBool || isInt || isDouble || isString,
+                       "Type is not supported for the settings object." );
+
+        if constexpr ( isBool )
+        {
+            return m_boolValues;
+        }
+        else if constexpr ( isInt )
+        {
+            return m_intValues;
+        }
+        else if constexpr ( isDouble )
+        {
+            return m_doubleValues;
+        }
+        else if constexpr ( isString )
+        {
+            return m_stringValues;
+        }
+    }
+
+    std::list<bool> m_boolValues;
+    std::list<int> m_intValues;
+    std::list<double> m_doubleValues;
+    std::list<std::string> m_stringValues;
+};
+} // namespace settings