...because swapping in the new standards-based implementation
leads to compile failures on tests to cover out-of-bounds cases.
Under the (wrong) assumption, that some mistake must be hidden in
the Splice-metafunction, I first provided a complete test coverage;
while the actual problem was right below my nose, and quite obvious...
The old implementation, being based on a case distinction over the argument count,
simply was not able even to notice excess arguments; other the new implementation,
based on variadics and `std::apply`, which is fully generic and thus
passes excess arguments to `std::bind` when a position beyond the actual
argument list is specified to be closed.
The old behaviour was to silently ignore such an out-of-bounds spec,
and this can be reinstated by explicitly capping the prepared tuple
of binders and actual arguments passed to `std::bind`
Another question of course is, if being tolerant here is a good idea.
And beyond that, function-closure.hpp is still terrifyingly complex,
unorganised and use-case driven, to start with....