Add wxUSE_STD_CONTAINERS and turn it on by default.

Previously, wxUSE_STL enabled both implicit conversion of wxString to
std::[w]string and use of standard containers for the implementation of their
wx equivalents. Split up the two roles now by allowing to enable the use of
the standard containers independently of (backwards incompatible) implicit
conversion in wxString and actually enable wxUSE_STD_CONTAINERS by default.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67343 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/string.h

@@ -1345,12 +1345,13 @@ public:
   }
 #endif // wxUSE_STRING_POS_CACHE
 
-  // even if we're not built with wxUSE_STL == 1 it is very convenient to allow
-  // implicit conversions from std::string to wxString and vice verse as this
-  // allows to use the same strings in non-GUI and GUI code, however we don't
-  // want to unconditionally add this ctor as it would make wx lib dependent on
-  // libstdc++ on some Linux versions which is bad, so instead we ask the
-  // client code to define this wxUSE_STD_STRING symbol if they need it
+  // even if we're not built with wxUSE_STD_STRING_CONV_IN_WXSTRING == 1 it is
+  // very convenient to allow implicit conversions from std::string to wxString
+  // and vice verse as this allows to use the same strings in non-GUI and GUI
+  // code, however we don't want to unconditionally add this ctor as it would
+  // make wx lib dependent on libstdc++ on some Linux versions which is bad, so
+  // instead we ask the client code to define this wxUSE_STD_STRING symbol if
+  // they need it
 #if wxUSE_STD_STRING
   #if wxUSE_UNICODE_WCHAR
     wxString(const wxStdWideString& str) : m_impl(str) {}
@@ -1368,10 +1369,8 @@ public:
   #endif
 #endif // wxUSE_STD_STRING
 
-  // Unlike ctor from std::string, we provide conversion to std::string only
-  // if wxUSE_STL and not merely wxUSE_STD_STRING (which is on by default),
-  // because it conflicts with operator const char/wchar_t* but we still
-  // provide explicit conversions to std::[w]string for convenience in any case
+  // Also always provide explicit conversions to std::[w]string in any case,
+  // see below for the implicit ones.
 #if wxUSE_STD_STRING
   // We can avoid a copy if we already use this string type internally,
   // otherwise we create a copy on the fly:
@@ -1408,13 +1407,14 @@ public:
     }
   #endif
 
-#if wxUSE_STL
-  // In wxUSE_STL case we also provide implicit conversions as there is no
-  // ambiguity with the const char/wchar_t* ones as they are disabled in this
-  // build (for consistency with std::basic_string<>)
+#if wxUSE_STD_STRING_CONV_IN_WXSTRING
+    // Implicit conversions to std::[w]string are not provided by default as
+    // they conflict with the implicit conversions to "const char/wchar_t *"
+    // which we use for backwards compatibility but do provide them if
+    // explicitly requested.
   operator wxStringToStdStringRetType() const { return ToStdString(); }
   operator wxStringToStdWstringRetType() const { return ToStdWstring(); }
-#endif // wxUSE_STL
+#endif // wxUSE_STD_STRING_CONV_IN_WXSTRING
 
 #undef wxStringToStdStringRetType
 #undef wxStringToStdWstringRetType
@@ -1654,11 +1654,12 @@ public:
     operator wxCStrData() const { return c_str(); }
 
     // the first two operators conflict with operators for conversion to
-    // std::string and they must be disabled in STL build; the next one only
-    // makes sense if conversions to char* are also defined and not defining it
-    // in STL build also helps us to get more clear error messages for the code
-    // which relies on implicit conversion to char* in STL build
-#if !wxUSE_STL
+    // std::string and they must be disabled if those conversions are enabled;
+    // the next one only makes sense if conversions to char* are also defined
+    // and not defining it in STL build also helps us to get more clear error
+    // messages for the code which relies on implicit conversion to char* in
+    // STL build
+#if !wxUSE_STD_STRING_CONV_IN_WXSTRING
     operator const char*() const { return c_str(); }
     operator const wchar_t*() const { return c_str(); }
 
@@ -1666,7 +1667,7 @@ public:
     // wxWidgets versions: this is the same as conversion to const char * so it
     // may fail!
     operator const void*() const { return c_str(); }
-#endif // wxUSE_STL
+#endif // !wxUSE_STD_STRING_CONV_IN_WXSTRING
 
     // identical to c_str(), for MFC compatibility
     const wxCStrData GetData() const { return c_str(); }