Resolve "Specify internal input/output dependencies of an Operation"

Closes #74 (closed)

b_asic/operation.py

@@ -180,6 +180,11 @@ class Operation(GraphComponent, SignalSourceProvider):
         """
         raise NotImplementedError
 
+    @abstractmethod
+    def inputs_required_for_output(self, output_index: int) -> Iterable[int]:
+        """Get the input indices of all inputs in this operation whose values are required in order to evalueate the output at the given output index."""
+        raise NotImplementedError
+
 
 class AbstractOperation(Operation, AbstractGraphComponent):
     """Generic abstract operation class which most implementations will derive from.
@@ -340,6 +345,11 @@ class AbstractOperation(Operation, AbstractGraphComponent):
             pass
         return [self]
 
+    def inputs_required_for_output(self, output_index: int) -> Iterable[int]:
+        if output_index < 0 or output_index >= self.output_count:
+            raise IndexError(f"Output index out of range (expected 0-{self.output_count - 1}, got {output_index})")
+        return [i for i in range(self.input_count)] # By default, assume each output depends on all inputs.
+
     @property
     def neighbors(self) -> Iterable[GraphComponent]:
         return list(self.input_signals) + list(self.output_signals)