cmake: Add an option for using std::string

With this basic_sstring is still available for code that needs the
extra features. It is just sstring that is aliased to std::string.

The default is still to use sstring.

Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>

CMakeLists.txt

@@ -48,6 +48,10 @@ option (Seastar_EXPERIMENTAL_COROUTINES_TS
   "Enable experimental support for Coroutines TS."
   OFF)
 
+option (Seastar_SSTRING
+  "Use seastar's own string implementation"
+  ON)
+
 set (Seastar_API_LEVEL
   "2"
   CACHE
@@ -745,6 +749,10 @@ if (Seastar_EXPERIMENTAL_COROUTINES_TS)
   target_compile_definitions (seastar PUBLIC SEASTAR_COROUTINES_TS)
 endif ()
 
+if (Seastar_SSTRING)
+  target_compile_options (seastar PUBLIC -DSEASTAR_SSTRING)
+endif ()
+
 if (Seastar_GCC6_CONCEPTS OR Concepts_FOUND)
   target_compile_definitions (seastar
     PUBLIC SEASTAR_HAVE_GCC6_CONCEPTS)

include/seastar/core/sstring.hh

@@ -42,7 +42,11 @@ namespace seastar {
 template <typename char_type, typename Size, Size max_size, bool NulTerminate = true>
 class basic_sstring;
 
+#ifdef SEASTAR_SSTRING
 using sstring = basic_sstring<char, uint32_t, 15>;
+#else
+using sstring = std::string;
+#endif
 
 template <typename char_type, typename Size, Size max_size, bool NulTerminate>
 class basic_sstring {