Use std::optional to allow optional inclusion of attributes

... instead of converting the O(U)String objects to char*.
Eventually this could allow to drop variants of *Element that take
XFastAttributeListRef.

Change-Id: Ib2748fcd93e655c55a176c00410fdcc7f052930d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/98179
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

1 files changed, 31 insertions, 10 deletions

diff --git a/include/sax/fshelper.hxx b/include/sax/fshelper.hxx
index 235181bf9846..e4b5072345e2 100644
--- a/include/sax/fshelper.hxx
+++ b/include/sax/fshelper.hxx
@@ -25,6 +25,7 @@
 #include <com/sun/star/uno/Sequence.hxx>
 #include <rtl/ustring.hxx>
 #include <sax/saxdllapi.h>
+#include <optional>
 #include <memory>
 #include <utility>
 
@@ -58,16 +59,21 @@ public:
         startElement(elementTokenId, std::forward<Args>(args)...);
     }
     template<typename... Args>
-    void startElement(sal_Int32 elementTokenId, sal_Int32 attribute, const OString& value, Args &&... args)
+    void startElement(sal_Int32 elementTokenId, sal_Int32 attribute,
+                      const std::optional<OString>& value, Args&&... args)
     {
-        pushAttributeValue(attribute, value);
+        if (value)
+            pushAttributeValue(attribute, *value);
         startElement(elementTokenId, std::forward<Args>(args)...);
     }
     template<typename... Args>
-    void startElement(sal_Int32 elementTokenId, sal_Int32 attribute, const OUString& value, Args&&... args)
+    void startElement(sal_Int32 elementTokenId, sal_Int32 attribute,
+                      const std::optional<OUString>& value, Args&&... args)
     {
-        // The temporary created by toUtf8() must stay alive until startElement() ends using it
-        startElement(elementTokenId, attribute, value.toUtf8(), std::forward<Args>(args)...);
+        std::optional<OString> opt;
+        if (value)
+            opt = value->toUtf8();
+        startElement(elementTokenId, attribute, opt, std::forward<Args>(args)...);
     }
     void startElement(sal_Int32 elementTokenId);
 
@@ -87,16 +93,21 @@ public:
         singleElement(elementTokenId, std::forward<Args>(args)...);
     }
     template<typename... Args>
-    void singleElement(sal_Int32 elementTokenId, sal_Int32 attribute, const OString& value, Args &&... args)
+    void singleElement(sal_Int32 elementTokenId, sal_Int32 attribute,
+                       const std::optional<OString>& value, Args&&... args)
     {
-        pushAttributeValue(attribute, value);
+        if (value)
+            pushAttributeValue(attribute, *value);
         singleElement(elementTokenId, std::forward<Args>(args)...);
     }
     template<typename... Args>
-    void singleElement(sal_Int32 elementTokenId, sal_Int32 attribute, const OUString& value, Args&&... args)
+    void singleElement(sal_Int32 elementTokenId, sal_Int32 attribute,
+                       const std::optional<OUString>& value, Args&&... args)
     {
-        // The temporary created by toUtf8() must stay alive until singleElement() ends using it
-        singleElement(elementTokenId, attribute, value.toUtf8(), std::forward<Args>(args)...);
+        std::optional<OString> opt;
+        if (value)
+            opt = value->toUtf8();
+        singleElement(elementTokenId, attribute, opt, std::forward<Args>(args)...);
     }
     void singleElement(sal_Int32 elementTokenId);
 
@@ -150,6 +161,16 @@ private:
 
 typedef std::shared_ptr< FastSerializerHelper > FSHelperPtr;
 
+// Helpers to make intention to pass optional attributes to *Element finctions explicit, instead of
+// using `(condition) ? value.toUtf8().getStr() : nullptr` syntax.
+inline const char* UseIf(const char* s, bool bUse) { return bUse ? s : nullptr; }
+// OString, OUString
+template<class TString>
+std::optional<TString> UseIf(const TString& s, bool bUse)
+{
+    return bUse ? std::optional<TString>(s) : std::optional<TString>();
+}
+
 }
 
 #endif // INCLUDED_SAX_FSHELPER_HXX