diff --git a/src/daglib/set.py b/src/daglib/set.py
index 90450f4..182a427 100644
--- a/src/daglib/set.py
+++ b/src/daglib/set.py
@@ -3,6 +3,8 @@ from __future__ import annotations
 from collections.abc import Callable, Iterable, Iterator, MutableSet
 from typing import Any, TypeVar
 
+from .util import ensure_set
+
 T = TypeVar("T")
 
 
@@ -15,18 +17,7 @@ class DAGSetView(MutableSet[T]):
     on_remove: Callable[[Any], None] | None = None
 
     def __init__(self, v: Iterable[T] | None = None) -> None:
-        match v:
-            case set():
-                pass
-            case str():
-                v = {v}
-            case Iterable():
-                v = set(v)
-            case None:
-                v = set()
-            case _:
-                v = {v}
-        self._data: set[T] = v
+        self._data: set[T] = ensure_set(v)
 
     # --- required MutableSet methods ---
 
@@ -52,62 +43,25 @@ class DAGSetView(MutableSet[T]):
 
     # --- in-place operator support ---
 
-    def __ior__(self, other: Iterable[T]) -> DAGSetView[T]:
-        # a |= b => union update
-        match other:
-            case str():
-                other = {other}
-            case Iterable():
-                other = set(other)
-            case _:
-                other = {other}
-        return super().__ior__(other)
-
     def __iadd__(self, other: Iterable[T]) -> DAGSetView[T]:
         # a += b => update/extend
-        match other:
-            case set():
-                self |= other
-            case str():
-                self |= {other}
-            case Iterable():
-                self |= set(other)
-            case _:
-                self |= {other}
+        self |= ensure_set(other)
         return self
 
+    def __ior__(self, other: Iterable[T]) -> DAGSetView[T]:
+        return super().__ior__(ensure_set(other))
+
     def __isub__(self, other: Iterable[T]) -> DAGSetView[T]:
         # a -= b => remove those in other
-        match other:
-            case str():
-                other = {other}
-            case Iterable():
-                other = set(other)
-            case _:
-                other = {other}
-        return super().__isub__(other)
+        return super().__isub__(ensure_set(other))
 
     def __iand__(self, other: Iterable[T]) -> DAGSetView[T]:
         # a &= b => keep only those also in other
-        match other:
-            case str():
-                other = {other}
-            case Iterable():
-                other = set(other)
-            case _:
-                other = {other}
-        return super().__iand__(other)
+        return super().__iand__(ensure_set(other))
 
     def __ixor__(self, other: Iterable[T]) -> DAGSetView[T]:
         # a ^= b => symmetric difference update
-        match other:
-            case str():
-                other = {other}
-            case Iterable():
-                other = set(other)
-            case _:
-                other = {other}
-        return super().__ixor__(other)
+        return super().__ixor__(ensure_set(other))
 
     # --- nice repr for debugging ---
 
diff --git a/src/daglib/util.py b/src/daglib/util.py
new file mode 100644
index 0000000..d77888f
--- /dev/null
+++ b/src/daglib/util.py
@@ -0,0 +1,17 @@
+from collections.abc import Iterable
+from typing import Any
+
+
+def ensure_set(x: Any) -> set:
+    """Convert x to a set if it isn't already."""
+    match x:
+        case set() as s:
+            return s
+        case str() as s:
+            return {s}
+        case Iterable() as it:
+            return set(it)
+        case None:
+            return set()
+        case _:
+            return {x}
diff --git a/tests/test_dag.py b/tests/test_dag.py
index 3e77ced..5072ffa 100644
--- a/tests/test_dag.py
+++ b/tests/test_dag.py
@@ -45,11 +45,19 @@ class TestDAGOps:
             assert "bar" in g._succ
             assert "baz" in g._succ["bar"]
             assert set(g["bar"]) == {"baz"}
-
             assert "bar" in g["foo"]
             assert "baz" in g["foo"]
             assert "baz" in g["bar"]
 
+        def test_dagsetview(self) -> None:
+            g = DAG[str]()
+            added = []
+            g.on_add = lambda u, v: added.append(v)
+            g["foo"] += {"bar", "baz"}
+            assert set(g["foo"]) == {"bar", "baz"}
+            assert "bar" in added
+            assert "baz" in added
+
         def test_self_loop_raises_error(self) -> None:
             g = DAG[str]()
             with pytest.raises(ValueError, match="Self-loops are not allowed"):
@@ -80,6 +88,15 @@ class TestDAGOps:
             with pytest.raises(KeyError):
                 g.remove_edge("foo", "bar", missing_ok=False)
 
+        def test_dagsetview(self) -> None:
+            g = DAG[str]()
+            g["foo"] += {"bar", "baz"}
+            removed = []
+            g.on_remove = lambda u, v: removed.append(v)
+            g["foo"] -= {"baz"}
+            assert set(g["foo"]) == {"bar"}
+            assert "baz" in removed
+
     class TestDAGDiscardNode:
         """Test node removal."""