[swappable.requirements] Consider to introduce Cpp17Swappable requirements as new editorial convenience requirement #5628
Description
The by far most often used "swappable" requirement used in the current normative wording has the style
lvalues of type T are swappable
defined in [swappable.requirements]. This is rather lengthy wording for a simple thing, and has caused editorial hiccups such as the one mentioned in #5627. I suggest introducing a new editorial vocabulary, Cpp17Swappable to be introduced in subclause [swappable.requirements], for example as follows:
A type
Xmeets the Cpp17Swappable requirements if lvalues of typeXare swappable.
just before line 5 defining the Cpp17ValueSwappable requirements and to replace using existing wording of the above mentioned form "lvalues of type T are swappable" by "T meets the Cpp17Swappable requirements".
This approach would be similar to the style used for other Cpp17 requirements and can be easily migrated into a collection of such requirements. For example, both bullets (5.1) and (5.2) of [unord.hash] could easily be merged into a single bullet of the form:
meet the Cpp17Hash requirements (Table 36), with Key as the function call argument type, the
Cpp17DefaultConstructible requirements (Table 29), the Cpp17CopyAssignable requirements (Table 33), the Cpp17Swappable requirements ([swappable.requirements]),
A similar and by far not last example is the potential merge of formatter.requirements] bullet (1.2) into the (1.1.x) sub-bullets, etc.
This particular wording form also matches quite well with syntactic requirements such as is_swappable_v versus the most general form is_swappable_with_v.
If this suggestion goes beyond an editorial action, please let me know, whether instead an official paper proposal would be preferred to realize these effects.