Implement string __hash__

src/stdlib/_string.pxd

@@ -142,3 +142,8 @@ cdef extern from "<string_view>" namespace "std" nogil:
         bint operator>= (const string_view&)
         bint operator>= (const char*)
 
+
+    cdef cppclass hash_string_view "std::hash<std::string_view>":
+        hash_string_view()
+        size_t operator() (const string_view&)
+

src/stdlib/string.pxd

-from stdlib._string cimport string_view
+from stdlib._string cimport string_view, hash_string_view
 from libc.string cimport strlen, strncpy
 from libc.stdlib cimport malloc, free
 
@@ -23,6 +23,9 @@ cdef cypclass Str:
     bint __eq__(self, Str other):
         return self._s == other._s
 
+    size_t __hash__(self):
+        return hash_string_view()(self._s)
+
     char __getitem__(self, int index) except 0:
         cdef int end = self._s.size()
         cdef int idx = index