On Mon, 19 Dec 2022 at 19:05, Lénárd Szolnoki <cpp_at_[hidden]>
wrote:

> Hi,
>
> On 19 December 2022 17:10:18 GMT, Edward Catmur <ecatmur_at_[hidden]>
> wrote:
> >On Mon, 19 Dec 2022 at 17:56, Lénárd Szolnoki via Std-Discussion <
> >std-discussion_at_[hidden]> wrote:
> >
> >> My reading in pseudocode it would look something like:
> >>
> >> /* ...comparing corresponding elements xi and yi in the expanded lists
> of
> >> subobjects for x and y (in increasing index order) until the first
> index i
> >> where xi == yi yields a result value which, when contextually converted
> to
> >> bool, yields false. */
> >> bool mismatch_found = false;
> >> for (size_t idx=0; idx < member_count; ++idx) {
> >> if (not (lhs_members[idx] == rhs_members[idx]) {
> >> mismatch_found = true;
> >> break;
> >> }
> >> }
> >>
> >> // If no such index exists, ...
> >> if (not mismatch_found) {
> >> return true; // ... V is true.
> >> } else { // Otherwise, ...
> >> return false; // ... V is false.
> >> }
> >>
> >> The first part describes the side effects of the defaulted definition,
> and
> >> the short-circuiting in particular. The second part describes the
> returned
> >> value.
> >>
> >> Obviously this can be written more clearly and concisely in pseudocode.
> >> Would be nice if it could similarly be simplified in English.
> >>
> >
> >Close, but `not` doesn't necessarily do what it should. I'd say this would
> >be more correct and idiomatic:
>
> Yes, you are right. At first I wanted to write !=, but then I "corrected"
> myself... It's pseudocode :)
>
> >/* ...comparing corresponding elements xi and yi in the expanded lists of
> >subobjects for x and y (in increasing index order) until the first index i
> >where xi == yi yields a result value which, when contextually converted to
> >bool, yields false. */
> >size_t idx=0;
> >for (; idx != member_count; ++idx) {
> > if (lhs_members[idx] == rhs_members[idx]) {
> > ;
> > } else {
> > break;
> > }
> >}
> >
> >// If no such index exists, ...
> >if (idx == member_count) {
> > return true; // ... V is true.
> >} else { // Otherwise, ...
> > return false; // ... V is false.
> >}
>
> I wonder if the English wording would be clearer if the if-else would be
> switched around.
>
> The current wording reads like:
>
> if (no such index exists) {
> V is true
> } else {
> V is false
> }
>
> I try to avoid if(!cond)...else in code, as now the else branch has a
> double negative.
>
> Replacing the last part of the wording with this might be clearer:
>
> "If such index exists, V is false. Otherwise V is true."
>

I think part of the reason for the current wording is that it parallels
that for spaceship, where the double negative does make sense:
https://eel.is/c++draft/class.compare#class.spaceship-3

Of course in real code I would just return from the loop on mismatch, but I
> don't know how to convey that in English.
>

It's tricky; English (and in particular Standardese) isn't really lent to
conveying that kind of algorithm. Quite honestly I don't feel that there's
much need to improve the wording; most people who read the specification
itself will know how to write a short-circuiting equality operator anyway,
so need only check that the wording can be read with that in mind.


> Cheers,
> Lénárd
>