On Monday, October 5, 2020 1:52:19 PM WEST Jean-Marc Lasgouttes wrote: > C++ stl uses unsigned for vector indices. > > JMarc
What the *man* has to say about that (pag. 123 from the article below): " The most contentious part of getting span into C++20 turned out to be the type of subscripts and sizes. The Core Guidelines span::size() was defined to return a signed int as opposed to the unsigned used by the standard-library containers. Similarly, subscripts were ints like for arrays, rather than unsigned as they are for standard-library containers. This led to a revival of an old and contentious issue: • Some consider it obvious that subscripts, being non-negative, should be represented as unsigned. • Some consider consistency with standard-library containers more important than any arguments about past mistakes related to unsigned. • Some consider the use of unsigned to represent non-negative numbers misguided (giving a false sense of safety) and a significant source of errors. Over the strenuous objections of the original designers (including me) and implementers of span, the second group won the votes, enthusiastically supported by the first group, so std::span has unsigned sizes and subscripts. I consider that a sad failure to take advantage of a rare opportunity to remedy a nasty old mistake [Stroustrup 2018e]. Somewhat predictably and not irrationally, the committee chose bug compatibility over the work of removing a significant bug source. But what could be wrong about representing subscripts as unsigned? This appears to be a rather emotional topic. I received several hate mails about this. There are two fundamental problems: • unsigned does not model natural numbers: it has modular arithmetic and subtraction. For example, if ch is an unsigned char, ch+100 will never overflow. • int and unsigned convert to each other at the slightest provocation, turning negative values into huge signed values and vice versa. For example, -2<2u is false; 2u is unsigned, so -2 is converted into a huge positive integer before the comparison." Thriving in a Crowded and Changing World: C++ 2006–2020 Bjarne Stroustrup Proc. ACM Program. Lang., Vol. 4, No. HOPL, Article 70. -- José Abílio -- lyx-devel mailing list lyx-devel@lists.lyx.org http://lists.lyx.org/mailman/listinfo/lyx-devel
