Move private methods implementation to header

src/core/qgsfeaturefiltermodel.cpp

@@ -464,13 +464,3 @@ void QgsFeatureFilterModel::setExtraIdentifierValue( const QVariant &extraIdenti
   mExtraIdentifierValue = extraIdentifierValue;
   emit extraIdentifierValueChanged();
 }
-
-QVariant QgsFieldExpressionValuesGatherer::data() const
-{
-  return mData;
-}
-
-void QgsFieldExpressionValuesGatherer::setData( const QVariant &data )
-{
-  mData = data;
-}

src/core/qgsfeaturefiltermodel_p.h

@@ -96,12 +96,18 @@ class QgsFieldExpressionValuesGatherer: public QThread
     /**
      * Internal data, use for whatever you want.
      */
-    QVariant data() const;
+    QVariant data() const
+    {
+      return mData;
+    }
 
     /**
      * Internal data, use for whatever you want.
      */
-    void setData( const QVariant &data );
+    void setData( const QVariant &data )
+    {
+      mData = data;
+    }
 
   signals: