Avoid COW overhead using css::uno::Sequence

The scenarios are:

1. Calling sequence's begin() and end() in pairs to pass to algorithms
   (both calls use getArray(), which does the COW checks)
2. In addition to #1, calling end() again when checking result of find
   algorithms, and/or begin() to calculate result's distance
3. Using non-const sequences in range-based for loops, which internally
   do #1
4. Assigning sequence to another sequence variable, and then modifying
   one of them

In many cases, the sequences could be made const, or treated as const
for the purposes of the algorithms (using std::as_const, std::cbegin,
and std::cend). Where algorithm modifies the sequence, it was changed
to only call getArray() once. For that, css::uno::toNonConstRange was
introduced, which returns a struct (sublclass of std::pair) with two
iterators [begin, end], that are calculated using one call to begin()
and one call to getLength().

To handle #4, css::uno::Sequence::swap was introduced, that swaps the
internal pointer to uno_Sequence. So when a local Sequence variable
should be assigned to another variable, and the latter will be modified
further, it's now possible to use swap instead, so the two sequences
are kept independent.

The modified places were found by temporarily removing non-const end().

Change-Id: I8fe2787f200eecb70744e8b77fbdf7a49653f628
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/123542
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/unotools/source/config/moduleoptions.cxx b/unotools/source/config/moduleoptions.cxx
index a4f4c509e839..26bdb65e4638 100644
--- a/unotools/source/config/moduleoptions.cxx
+++ b/unotools/source/config/moduleoptions.cxx
@@ -738,16 +738,14 @@ void SvtModuleOptions_Impl::MakeReadonlyStatesAvailable()
         return;
 
     css::uno::Sequence< OUString > lFactories = GetNodeNames(OUString());
-    std::transform(lFactories.begin(), lFactories.end(), lFactories.begin(),
-        [](const OUString& rFactory) -> OUString {
-            return rFactory + PATHSEPARATOR PROPERTYNAME_DEFAULTFILTER;
-        });
+    for (OUString& rFactory : toNonConstRange(lFactories))
+        rFactory += PATHSEPARATOR PROPERTYNAME_DEFAULTFILTER;
 
     css::uno::Sequence< sal_Bool > lReadonlyStates = GetReadOnlyStates(lFactories);
     sal_Int32 c = lFactories.getLength();
     for (sal_Int32 i=0; i<c; ++i)
     {
-        OUString&            rFactoryName = lFactories[i];
+        const OUString&            rFactoryName = std::as_const(lFactories)[i];
         SvtModuleOptions::EFactory  eFactory;
 
         if (!ClassifyFactoryByName(rFactoryName, eFactory))