add is_string<T>

support all basic_string types
add note about filtered_hash<T> whitelist

2 files changed, 26 insertions, 14 deletions

diff --git a/Rx/v2/src/rxcpp/rx-observable.hpp b/Rx/v2/src/rxcpp/rx-observable.hpp
index bbc0274..e2646ed 100644
--- a/Rx/v2/src/rxcpp/rx-observable.hpp
+++ b/Rx/v2/src/rxcpp/rx-observable.hpp
@@ -824,7 +824,7 @@ public:
         \param s  the selector function
 
         \return  Observable that emits the items from the source observable, transformed by the specified function.
-
+        
         \sample
         \snippet map.cpp map sample
         \snippet output.txt map sample
@@ -886,6 +886,8 @@ public:
 
         \return  Observable that emits those items from the source observable that are distinct.
 
+        \note distinct keeps an unordered_set<T> of past values. Due to an issue in multiple implementations of std::hash<T>, rxcpp maintains a whitelist of hashable types. new types can be added by specializing rxcpp::filtered_hash<T>
+
         \sample
         \snippet distinct.cpp distinct sample
         \snippet output.txt distinct sample
diff --git a/Rx/v2/src/rxcpp/rx-util.hpp b/Rx/v2/src/rxcpp/rx-util.hpp
index 233049e..d25b76f 100644
--- a/Rx/v2/src/rxcpp/rx-util.hpp
+++ b/Rx/v2/src/rxcpp/rx-util.hpp
@@ -674,18 +674,37 @@ public:
 };
 #endif
 
+template<typename, typename C = types_checked>
+struct is_string : std::false_type {
+};
+
+template <typename T>
+struct is_string<T, 
+    typename types_checked_from<
+        typename T::value_type,
+        typename T::traits_type,
+        typename T::allocator_type>::type>
+    : std::is_base_of<
+            std::basic_string<
+                typename T::value_type,
+                typename T::traits_type,
+                typename T::allocator_type>, T> {
+};
+
 }
 namespace rxu=util;
 
+
 //
 // due to an noisy static_assert issue in more than one std lib impl, 
-// build a whitelist filter for the types that are allowed to be hashed 
-// in rxcpp. this allows is_hashable<T> to work.
+// rxcpp maintains a whitelist filter for the types that are allowed 
+// to be hashed. this allows is_hashable<T> to work.
 //
 // NOTE: this should eventually be removed!
 //
 template <class T, typename = void> 
 struct filtered_hash;
+
 template <class T> 
 struct filtered_hash<T, typename std::enable_if<std::is_enum<T>::value>::type> : std::hash<T> {
 };
@@ -695,17 +714,8 @@ struct filtered_hash<T, typename std::enable_if<std::is_integral<T>::value>::typ
 template <class T> 
 struct filtered_hash<T, typename std::enable_if<std::is_pointer<T>::value>::type> : std::hash<T> {
 };
-template <class T>
-struct filtered_hash<T, typename std::enable_if<std::is_same<std::string, T>::value>::type> : std::hash<T> {
-};
-template <class T>
-struct filtered_hash<T, typename std::enable_if<std::is_same<std::wstring, T>::value>::type> : std::hash<T> {
-};
-template <class T>
-struct filtered_hash<T, typename std::enable_if<std::is_same<std::u16string, T>::value>::type> : std::hash<T> {
-};
-template <class T>
-struct filtered_hash<T, typename std::enable_if<std::is_same<std::u32string, T>::value>::type> : std::hash<T> {
+template <class T> 
+struct filtered_hash<T, typename std::enable_if<rxu::is_string<T>::value>::type> : std::hash<T> {
 };
 
 template<typename, typename C = rxu::types_checked>