I don't like the idea of removing the "bool isSlice" argument from the
*SubscriptTransform() function pointer. This patch series should make
only minimal changes to the subscripting API. While it's true that
each implementation can easily determine the boolean value of isSlice
itself, I don't see a clear benefit to changing the interface. As you
noted, arrsubs cares about isSlice; and users can also define custom
data types that support subscripting, so the interface is not limited
to built-in types.
As the comment for *SubscriptTransform() explains:
(Of course, if the transform method
* does not care to support slicing, it can just throw an error if isSlice.)
It's possible that in the end the "isSlice" argument isn't needed at
all, but I don’t think this patch set is the right place for that
refactor.
I agree we should keep the change minimum and tightly related to the core feature.
My original suggestion was to move
/*
* Detect whether any of the indirection items are slice specifiers.
*
* A list containing only simple subscripts refers to a single container
* element. If any of the items are slice specifiers (lower:upper), then
* the subscript expression means a container slice operation.
*/
foreach(idx, *indirection)
{
Node *ai = lfirst(idx);
if (IsA(ai, A_Indices) && castNode(A_Indices, ai)->is_slice)
{
isSlice = true;
break;
}
}
To out of transformContainerSubscripts(). Because the function was called only once under “if”, now this patch change it to be called under “while”, which brings two issues:
* Original it was O(n) as it was under “if”, now it is O(n2) as it is under “while”.
* Logically it feels wrong now. Because this loops over the entire indirection list to check is_slice, while the subsequent sbsroutines->transform() may only process a portion (prefix) of indirection list. Say, the 5th element is slice, but the first sbsroutines-transform() call will only process the first 3 elements of indirection list, then pass true to the first transform() call sounds wrong.
if we pull the loop out of transformContainerSubscripts(), then we have to add a new parameter “bool is_slice” to it. But after some researching, I found that making that change is more complicated than removing “is_slice” parameter from SubscriptTransform(). That’s why I ended up suggesting removing “is_slice” from SubscriptTransform().
Does that sound reasonable?
