Fix bug in unquote

plum/util.py

@@ -136,12 +136,16 @@ def check_future_annotations(frame=None):
 def unquote(x):
     """Remove quotes from a string at the outermost level.
 
+    If `x` is not a string, `x` is returned immediately.
+
     Args:
-        x (str): String to remove quotes from.
+        x (str or object): String to remove quotes from.
 
     Return:
-        str: `x` but without quotes.
+        str or object: `x` but without quotes.
     """
+    if not isinstance(x, str):
+        return x
     while len(x) >= 2 and x[0] == x[-1] and x[0] in {'"', "'"}:
         x = x[1:-1]
     return x

tests/dispatcher/test_future_annotations.py

@@ -49,10 +49,18 @@ def f(x: int):
     with pytest.raises(NotFoundLookupError):
         f("1")
 
-    @f.dispatch
-    def f(x: str):
+    def g(x: str):
         return "str"
 
+    f.dispatch(g)
+
+    assert f(1) == "int"
+    assert f("1") == "str"
+
+    # Extending `f` again will cause `g`s type hints to be processed again, which should
+    # now be types rather than strings. We check that this also works.
+    f.dispatch(g)
+
     assert f(1) == "int"
     assert f("1") == "str"