Fixed sfg being immutable when replacing operations

b_asic/signal_flow_graph.py

@@ -444,7 +444,7 @@ class SFG(AbstractOperation):
                 _signal.remove_source()
                 _signal.set_source(operation.output(index_out))
        
-        return _sfg
+        return _sfg()
 
     def _evaluate_source(self, src: OutputPort, results: MutableResultMap, registers: MutableRegisterMap, prefix: str) -> Number:
         src_prefix = prefix

test/test_sfg.py

@@ -274,13 +274,13 @@ class TestReplaceOperations:
     def test_replace_neg_add_with_sub(self):
         in1 = Input()
         in2 = Input()
-        neg1 = ConstantMultiplication(-1, in1, 'neg1')
+        neg1 = ConstantMultiplication(-1, in1)
         add1 = neg1 + in2
         out1 = Output(add1)
         sfg = SFG(inputs=[in1, in2], outputs=[out1])
 
         sub1 = Subtraction()
-        _sfg = sfg.replace_operations(['add1', 'neg1'], sub1)
+        _sfg = sfg.replace_operations(['add1', 'cmul1'], sub1)
 
         assert 'sub1' in _sfg._components_by_id.keys()
         assert {add1, neg1} not in _sfg.operations