conform
  to the 2011 C++ standard which forbids Copy-On-Write strings and requires
  lists to keep track of their size.
</p><p> In order to maintain backwards compatibility for existing code linked
  to libstdc++ the library's soname has not changed and the old
  implementations are still supported in parallel with the new ones.
  This is achieved by defining the new implementations in an inline namespace
  so they have different names for linkage purposes, e.g. the new version of
  <code class="classname"