Use property

equinox/_jit.py

@@ -274,7 +274,7 @@ def f(x, y):  # both args traced if arrays, static if non-arrays
             "`jitkwargs` cannot contain 'static_argnums', 'static_argnames' or "
             "'donate_argnums'"
         )
-    signature = inspect.signature(fun.__call__)
+    signature = inspect.signature(fun)
 
     if donate not in {"all", "warn", "none"}:
         raise ValueError(

equinox/_module.py

@@ -317,11 +317,6 @@ def __init__(self, *args, **kwargs):
             # TODO: is this next line still necessary?
             cls.__init__.__module__ = cls.__module__
 
-        # Assign __signature__ to match dataclass
-        sig = inspect.signature(cls.__init__)
-        params = list(sig.parameters.values())[1:]  # Remove self to match dataclass sig
-        cls.__signature__ = sig.replace(parameters=params)
-
         # [Step 5] We support an optional `strict` mode for Rust-like strictness in the
         # type checking.
         # In practice this is probably too much for your average user, but it's a great
@@ -436,6 +431,13 @@ def __init__(self, *args, **kwargs):
         # Done!
         return cls
 
+    @property
+    def __signature__(cls):
+        # Use signature of __init__ method for non-callable equinox modules
+        sig = inspect.signature(cls.__init__)
+        params = list(sig.parameters.values())[1:]  # Remove self parameter
+        return sig.replace(parameters=params)
+
     # This method is called whenever you initialise a module: `MyModule(...)`
     def __call__(cls, *args, **kwargs):
         if _is_force_abstract[cls]:

tests/test_module.py

@@ -993,22 +993,46 @@ class ExampleModel(eqx.Module):
     assert static_field.metadata == dict(foo=False, static=True)
 
 
-def test_signature():
-    class Foo(eqx.Module):
+def signature_test_cases():
+    @dataclasses.dataclass
+    class FooDataClass:
+        a: int
+
+    class FooModule(eqx.Module):
         a: int
 
+    @dataclasses.dataclass
+    class CustomInitDataClass:
+        def __init__(self, a: int):
+            pass
+
     class CustomInitModule(eqx.Module):
+        def __init__(self, a: int):
+            pass
+
+    @dataclasses.dataclass
+    class CallableDataClass:
         a: int
 
-        def __init__(self, b: int):
-            self.a = b
+        def __call__(self, b: int):
+            pass
 
-    class FooCallable(eqx.Module):
+    class CallableModule(eqx.Module):
         a: int
 
         def __call__(self, b: int):
             pass
 
-    for T in [Foo, FooCallable, CustomInitModule, FooCallable(1)]:
-        print(str(T))
-        print(str(inspect.signature(T)))
+    test_cases = [
+        (FooDataClass, FooModule),
+        (CustomInitDataClass, CustomInitModule),
+        (CallableDataClass, CallableModule),
+        (CallableDataClass(1), CallableModule(1)),
+    ]
+    return test_cases
+
+
+@pytest.mark.parametrize(("dataclass", "module"), signature_test_cases())
+def test_signature(dataclass, module):
+    # Check module signature matches dataclass signatures.
+    assert inspect.signature(dataclass) == inspect.signature(module)