[Python-Dev] Adding NewType() to PEP 484 (original) (raw)

Glenn Linderman v+python at g.nevcal.com
Tue May 31 20:46:38 EDT 2016

On 5/31/2016 4:58 PM, Nick Coghlan wrote:

On 31 May 2016 3:12 pm, "Glenn Linderman" <v+python at g.nevcal.com_ _<mailto:v%2Bpython at g.nevcal.com>> wrote: > > On 5/31/2016 12:55 PM, rndblnch wrote: >> >> Guido van Rossum <gvanrossum gmail.com <http://gmail.com>> writes: >> >>> >>> Also -- the most important thing. What to call these things? We're >>> pretty much settled on the semantics and how to create them (A = >>> NewType('A', int)) but what should we call types like A when we're >>> talking about them? "New types" sounds awkward. >> >> back in high school, i was introduced to c programming with the "disciplined >> C" preprocessor [0]. >> it made the distinction between information type and representation type >> (e.g. between the semantic and the implementation). >> those new types where created using typedefs and were named 'parallel types' >> below is the relevant part of the dcc presentation: > > > Interesting! Prior art. And parallel type isn't a bad name... If I heard "parallel type", I'd assume it had something to do with parallel processing.

Google seems to think so also... "Disciplined C" probably predates parallel processing, but adding disciplined C preprocessor to the search does find a document about the preprocessor in the same sense used by @rndblnch. And the types do have "parallel" behavior... every behavior of one is found identically in the other. So it makes sense, but it would be hard to find the prior art without extra information, as the term is now overwhelmed by "Parallel Type-checking" for parallel processing.

Still, some mention should probably be made of "parallel type in the 'Disciplined C preprocessor' " in the "prior art" category of PEP 484.

From reading about Disciplined C, would seem that this feature could be used as a foundation to add "units" support to variables, validated only by a type checker, and thus having no runtime overhead, although it would take some more features from Disciplined C, regarding the definition of legal combinations of types and operations.

Of the options suggested so far, DistinctType seems the most promising to me.

Cheers, Nick. > >> >> >> """ >> a major innovation of Disciplined C is the notion of "parallel type", that >> allows a distinction between information type and representation type. The >> following: >> >> typedef int Tindex, Tval; >> typedef Tindex Trow, Tcol; >> >> creates four distinct types, but which all accept the same operations and >> the same constants as the "representation" type ('int' here). Tindex, Tval, >> Trow and Tcol are examples of "information" types, because they convey an >> idea of the semantics of the corresponding objects. For example, they may be >> put to use in a checkers playing program: Tval will name 'int's that >> represent values of checkers, Trow and Tcol, 'int's that represent row and >> column indexes, Tindex, generic type for indexes. >> Tindex, Tval, Trow and Tcol are called parallel types; in fact, a type T1 is >> said to be parallel to a type T2 iff both are defined through a chain of >> typedefs starting from the same 'baseType', with no intervening qualifier >> nor modifier (pointer/array/function decla- rator, see grammar in Appendix >> A). In other words, T and T2 must be strict synonyms of baseType. >> """ >> >> renaud >> >> 0. Disciplined C >> >> ACM SIGPLAN Notices Homepage archive >> Volume 30 Issue 12, Dec. 1995 >> Pages 43 - 50 >> http://dl.acm.org/citation.cfm?id=219726.219747 >> http://www.digiater.nl/openvms/freeware/v50/dcc/dcc-v27d/dccarticle.ps >> _>> ________________________ >> Python-Dev mailing list >> Python-Dev at python.org <mailto:Python-Dev at python.org> >> https://mail.python.org/mailman/listinfo/python-dev >> Unsubscribe: https://mail.python.org/mailman/options/python-dev/v%2Bpython%40g.nevcal.com >> > > _> ________________________ > Python-Dev mailing list > Python-Dev at python.org <mailto:Python-Dev at python.org> > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ncoghlan%40gmail.com >

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