Add options "stored_size" and "growth_factor" options to string. Make string's default growth factor the same as vector's (60%)

Author: igaztanaga

include/boost/container/container_fwd.hpp

@@ -272,8 +272,9 @@ struct small_flat_multimap_of
 };
 
 template <class CharT
-         ,class Traits = std::char_traits<CharT>
-         ,class Allocator  = void >
+         ,class Traits     = std::char_traits<CharT>
+         ,class Allocator  = void
+         ,class Options    = void >
 class basic_string;
 
 typedef basic_string <char>   string;

include/boost/container/detail/next_capacity.hpp

@@ -84,10 +84,18 @@ inline void clamp_by_stored_size_type(SizeType &, SizeType)
 template<class SizeType, class SomeStoredSizeType>
 inline void clamp_by_stored_size_type(SizeType &s, SomeStoredSizeType)
 {
-   if (s >= SomeStoredSizeType(-1) ) 
+   if (s > SomeStoredSizeType(-1) ) 
       s = SomeStoredSizeType(-1);
 }
 
+template<class SizeType, class SomeStoredSizeType>
+inline void clamp_by_half_stored_size_type(SizeType &s, SomeStoredSizeType)
+{
+   const SizeType half_max = SizeType(SomeStoredSizeType(-1)) >> 1u;
+   if (s > half_max ) 
+      s = half_max;
+}
+
 }  //namespace container {
 }  //namespace boost {
 

include/boost/container/options.hpp

@@ -244,6 +244,26 @@ class default_next_capacity;
 
 typedef vector_opt<void, void> vector_null_opt;
 
+template<class GrowthType, class StoredSizeType>
+struct string_opt
+{
+   typedef GrowthType      growth_factor_type;
+   typedef StoredSizeType  stored_size_type;
+
+   template<class AllocTraits>
+   struct get_stored_size_type
+      : get_stored_size_type_with_alloctraits<AllocTraits, StoredSizeType>
+   {};
+};
+
+typedef string_opt<void, void> string_null_opt;
+
+struct growth_factor_50;
+
+struct growth_factor_60;
+
+struct growth_factor_100;
+
 #else
 
 //!This growth factor argument specifies that the container should increase its
@@ -674,6 +694,40 @@ using deque_options_t = typename boost::container::deque_options<Options...>::ty
 
 #endif
 
+//! Helper metafunction to combine options into a single type to be used
+//! by \c boost::container::string.
+//! Supported options are: \c boost::container::growth_factor and \c boost::container::stored_size
+#if defined(BOOST_CONTAINER_DOXYGEN_INVOKED) || defined(BOOST_CONTAINER_VARIADIC_TEMPLATES)
+template<class ...Options>
+#else
+template<class O1 = void, class O2 = void, class O3 = void, class O4 = void>
+#endif
+struct string_options
+{
+   /// @cond
+   typedef typename ::boost::intrusive::pack_options
+      < string_null_opt,
+      #if !defined(BOOST_CONTAINER_VARIADIC_TEMPLATES)
+      O1, O2, O3, O4
+      #else
+      Options...
+      #endif
+      >::type packed_options;
+   typedef string_opt< typename packed_options::growth_factor_type
+                     , typename packed_options::stored_size_type> implementation_defined;
+   /// @endcond
+   typedef implementation_defined type;
+};
+
+#if !defined(BOOST_NO_CXX11_TEMPLATE_ALIASES)
+
+//! Helper alias metafunction to combine options into a single type to be used
+//! by \c boost::container::string.
+template<class ...Options>
+using string_options_t = typename boost::container::string_options<Options...>::type;
+
+#endif
+
 //!This option specifies the maximum size of a block in bytes: this delimites the number of contiguous elements
 //!that will be allocated by some containers as min(1u, BlockBytes/sizeof(value_type))
 //!A value zero represents the default value.