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

[Glenn Linderman]

On 5/31/2016 12:55 PM, rndblnch wrote:
> Guido van Rossum <gvanrossum <at> 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...

>
> """
> 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-v2_7d/dccarticle.ps
>
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