Re: [boost] Adding logical implication to boost

pon., 6 sty 2025 o 19:43 Ivan Matek via Boost napisał(a):

On Sun, Jan 5, 2025 at 3:27 PM Traian Enache wrote:

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In my work, whenever I’ve had to do logical implications, I always naturally used ‘!a || b’, not once has the thought of “geez, wish C++ had => for logical implication” crossed my mind.

As I said I agree with regards to =>. In regards to boost::implies vs !a || b my belief is that it heavily depends on the person. For me (and I presume many others even if we are not majority) even after many years of programming if I saw something like boost::implies(student.graduaded(), student.num_active_courses() == 0) reads much much nicer than !student.graduaded() || student.num_active_courses() == 0

So I am not trying to covert anybody to prefer implies function call, but I feel there is large number of people that would prefer a helper. As mentioned in the paper there is also the thing with the short circuit evaluation if second argument is invocable returning bool.

If you are only interested in a convenience function (and not the short-circuiting properties), this reminds me of Peter Dimov's remark about operator =>: It already exists in C++ and is spelled operator <=. Regards, &rzej;

P.S. if you do not mind sharing details about your usecases I wonder when did you find use for implication?.

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Regarding the location for a logical_implication<> function, I’d advocate for either Boost.Algorithm or Boost.Functional, given that the std::logical_XXX<> class templates are placed in the <functional> header; even if it would be a mouthful to say and type, I don’t expect it to be seen very often.

Regarding <functional> header I do not think it fits there primarily, although I can imagine that is where std::logical_implication will be added in C++. For me they are there and exist because in C++ we can not pass operators to algorithms, e.g. std::accumulate(a.begin(), a.end(), 1, *), but this seems like a generic helper function because unlike && and || we have no operator for it. So I think it may be useful to add it in a way that enables one to pass it around(although I never had need to do this) but primary use is to just immediately invoke it yourself. I may be missing something, but this is my current thinking.

On Mon, Jan 6, 2025 at 12:43 PM Richard Hodges via Boost < boost@lists.boost.org> wrote:

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C++ standardisation seems to have jumped the shark.

I was just mentioning the proposal for context, so not sure this is super related to helper function, but I do not think this will get standardized, for example Walter in 2013 had swap operator :=: proposal.

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