diff --git a/src/faebryk/core/moduleinterface.py b/src/faebryk/core/moduleinterface.py
index 8c70ced3..ae3f0c7c 100644
--- a/src/faebryk/core/moduleinterface.py
+++ b/src/faebryk/core/moduleinterface.py
@@ -22,7 +22,7 @@
 )
 from faebryk.core.node import Node
 from faebryk.core.trait import Trait
-from faebryk.libs.util import print_stack
+from faebryk.libs.util import once, print_stack
 
 logger = logging.getLogger(__name__)
 
@@ -118,6 +118,7 @@ class TraitT(Trait): ...
 
     # TODO rename
     @classmethod
+    @once
     def LinkDirectShallow(cls):
         """
         Make link that only connects up but not down
@@ -130,13 +131,11 @@ class _LinkDirectShallowMif(
             LinkDirectShallow(lambda link, gif: test(gif.node))
         ): ...
 
-        return _LinkDirectShallowMif
+        print("Make shallow for", cls)
 
-    _LinkDirectShallow: type[_TLinkDirectShallow] | None = None
+        return _LinkDirectShallowMif
 
-    def __preinit__(self) -> None:
-        if not type(self)._LinkDirectShallow:
-            type(self)._LinkDirectShallow = type(self).LinkDirectShallow()
+    def __preinit__(self) -> None: ...
 
     def _connect_siblings_and_connections(
         self, other: "ModuleInterface", linkcls: type[Link]
@@ -335,7 +334,7 @@ def connect_via(
             intf.connect(other, linkcls=linkcls)
 
     def connect_shallow(self, other: Self) -> Self:
-        return self.connect(other, linkcls=type(self)._LinkDirectShallow)
+        return self.connect(other, linkcls=type(self).LinkDirectShallow())
 
     def is_connected_to(self, other: "ModuleInterface"):
         return self.connected.is_connected(other.connected)
diff --git a/src/faebryk/libs/util.py b/src/faebryk/libs/util.py
index 8f68a717..10266b89 100644
--- a/src/faebryk/libs/util.py
+++ b/src/faebryk/libs/util.py
@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: MIT
 
 import asyncio
+import functools
 import inspect
 import logging
 from abc import abstractmethod
@@ -797,3 +798,20 @@ def __() -> T:
         return __
 
     return _
+
+
+def once[T, **P](f: Callable[P, T]) -> Callable[P, T]:
+    class _once:
+        def __init__(self) -> None:
+            self.cache = {}
+
+        def __call__(self, *args: P.args, **kwds: P.kwargs) -> Any:
+            lookup = (args, tuple(kwds.items()))
+            if lookup in self.cache:
+                return self.cache[lookup]
+
+            result = f(*args, **kwds)
+            self.cache[lookup] = result
+            return result
+
+    return _once()
diff --git a/test/core/test_hierarchy_connect.py b/test/core/test_hierarchy_connect.py
index 559d3596..ed9e78b9 100644
--- a/test/core/test_hierarchy_connect.py
+++ b/test/core/test_hierarchy_connect.py
@@ -79,6 +79,11 @@ def test_chains(self):
     def test_bridge(self):
         self_ = self
 
+        # U1 ---> _________B________ ---> U2
+        #  TX          IL ===> OL          TX
+        #   S -->  I -> S       S -> O -->  S
+        #   R --------  R ----- R --------  R
+
         class Buffer(Module):
             ins = L.if_list(2, F.Electrical)
             outs = L.if_list(2, F.Electrical)
@@ -171,12 +176,18 @@ def _assert_link(mif1: ModuleInterface, mif2: ModuleInterface, link=None):
         )
         _assert_link(buf.ins_l[0].reference, buf.outs_l[0].reference)
         _assert_link(buf.outs_l[1].reference, buf.ins_l[0].reference)
-
         _assert_link(bus1.rx.reference, bus2.rx.reference, LinkDirect)
 
+        # connect through up
+        _assert_link(bus1.tx, buf.ins_l[0], LinkDirect)
+        _assert_link(bus2.tx, buf.outs_l[0], LinkDirect)
+
+        # connect shallow
+        _assert_link(buf.ins_l[0], buf.outs_l[0], _TLinkDirectShallow)
+
         # Check that the two buffer sides are connected logically
-        _assert_link(bus1.rx, bus2.rx)
         _assert_link(bus1.tx, bus2.tx)
+        _assert_link(bus1.rx, bus2.rx)
         _assert_link(bus1, bus2)
 
     def test_specialize(self):
@@ -222,7 +233,4 @@ class _Link(LinkDirectShallow(lambda link, gif: True)): ...
 
 
 if __name__ == "__main__":
-    # unittest.main()
-    import typer
-
-    typer.run(TestHierarchy().test_bridge)
+    unittest.main()
diff --git a/test/libs/util.py b/test/libs/util.py
index 97c3fb37..445c4bf6 100644
--- a/test/libs/util.py
+++ b/test/libs/util.py
@@ -5,7 +5,7 @@
 from itertools import combinations
 
 from faebryk.libs.logging import setup_basic_logging
-from faebryk.libs.util import SharedReference, zip_non_locked
+from faebryk.libs.util import SharedReference, once, zip_non_locked
 
 
 class TestUtil(unittest.TestCase):
@@ -54,6 +54,44 @@ def all_equal(*args: SharedReference):
 
         all_equal(r1, r2, r3, r4, r5)
 
+    def test_once(self):
+        global ran
+        ran = False
+
+        @once
+        def do(val: int):
+            global ran
+            ran = True
+            return val
+
+        self.assertFalse(ran)
+
+        self.assertEqual(do(5), 5)
+        self.assertTrue(ran)
+        ran = False
+
+        self.assertEqual(do(5), 5)
+        self.assertFalse(ran)
+
+        self.assertEqual(do(6), 6)
+        self.assertTrue(ran)
+        ran = False
+
+        class A:
+            @classmethod
+            @once
+            def do(cls):
+                global ran
+                ran = True
+                return cls
+
+        self.assertEqual(A.do(), A)
+        self.assertTrue(ran)
+        ran = False
+
+        self.assertEqual(A.do(), A)
+        self.assertFalse(ran)
+
 
 if __name__ == "__main__":
     setup_basic_logging()