[pypy-dev] Avoiding code duplication

Antonio Cuni anto.cuni at gmail.com
Sat Apr 15 12:59:07 CEST 2006

Armin Rigo wrote:
> I think this is kind-of-reasonable.  The ADT method approach of the
> lltypesystem was introduced late during the development of the rtyper;
> by now, it would be reasonable to define common method names between the
> ADT methods of the lltypesystem and the GENERIC_METHODS of the
> ootypesystem.
> I am unsure about the performance penalty.  The current version of many
> ll helpers, for example, read the 'items' pointer only once and reuse
> it; if this gets replaced by ADT methods like 'getitem_nonneg()', it
> means that althought the call is probably inlined there is still the
> overhead of reading 'items' through each iteration in the list.  Who
> knows, maybe C compilers will notice and move the read out of the loop.
> Just give it a try on a small example like ll_listindex(), I guess...

as we decided on #pypy I've changed the ADT interface. As I wrote in the 
commit log:

The interface of ListRepr and FixedSizeListRepr has changed: two
accessor methods has been added: ll_getitem_fast and
ll_setitem_fast. They should be used instead of the ll_items()[index]
idiom: that way when ootypesystem's list will support that interface
we will able to write function useable with both typesystem with no

The various ll_* helper function has been adapted to use the new
interface. Moreover function that accessed directly to the "l.length"
field has been changed to call the "ll_length()" method instead, for
the same reasons as above.

The next step is to rename ootypesystem's list _GENERIC_METHODS to match 
the ADT methods in lltypesystem's list, then we could try to share most 
of ll_* function that currently belongs only to lltypesystem/rlist.py.
I hope I will do it tomorrow.

> A different comment: as you mentioned on IRC it would be nice if the
> back-end could choose which methods it implements natively.  At one
> point there was the idea that maybe the 'oopspec' attributes that
> started to show up in lltypesystem/rlist.py (used by the JIT only) could
> be useful in this respect.  If I remember correctly, the idea didn't
> work out because of the different 'lowleveltype' needed, and the
> difference in the interface.  Merging the ADT method names of lltyped
> lists and the GENERIC_METHODS of ootyped lists could be a step in this
> direction again.  The interesting point is that each oo back-end could
> then choose to special-case the ll_xxx() functions with the oopspecs
> that they recognize, and just translate the other ones normally.  (The
> ll back-ends always translate them all.)

I saw that 'oopspec' attributes, but I didn't understand the exact 
semantic; your proposal sounds reasonable to me: if I can figure out 
correctly this way the typesystem specific code would be reduced to the 
minimum and will help to port other Repr such as rdict to ootypesystem, 
too. I'll investigate a bit in this direction as soon as I can.

good Easter to all,
ciao Anto

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