Re: Adding logical implication to boost

From: Ivan Matek (libbooze_at_[hidden])
Date: 2025-01-06 18:43:15

On Sun, Jan 5, 2025 at 3:27 PM Traian Enache <ena.traian_at_[hidden]> wrote:

> 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.

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

> 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_at_[hidden]> wrote:

> 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.