mpi: Fixup deterministic MPI code generation

Author: FabioLuporini

devito/mpi/halo_scheme.py

@@ -31,17 +31,14 @@ class HaloSchemeEntry(EnrichedTuple):
 
     __rargs__ = ('loc_indices', 'loc_dirs', 'halos', 'dims')
 
-    def __init__(self, loc_indices, loc_dirs, halos, dims, getters=None):
-        self.loc_indices = frozendict(loc_indices)
-        self.loc_dirs = frozendict(loc_dirs)
-        self.halos = frozenset(halos)
-        self.dims = frozenset(dims)
+    def __new__(cls, loc_indices, loc_dirs, halos, dims, getters=None):
+        items = [frozendict(loc_indices), frozendict(loc_dirs),
+                 frozenset(halos), frozenset(dims)]
+        kwargs = dict(zip(cls.__rargs__, items))
+        return super().__new__(cls, *items, getters=cls.__rargs__, **kwargs)
 
     def __hash__(self):
-        return hash((self.loc_indices,
-                     self.loc_dirs,
-                     self.halos,
-                     self.dims))
+        return hash((self.loc_indices, self.loc_dirs, self.halos, self.dims))
 
     def union(self, other):
         """