Now looking into largely obsolete library facilities...
Starting from `ScopedHolder`, I found a surprising problem with ''perfect forwarding....''
...which however turned out to be the result of ''sloppy programming'' on my side.
At that time, in 2017, seemingly I was under pressure to define a Session-Command,
which captures a Time-entity as »State Memento«. Which turned out to be impossible,
since the Time entities were conceived as being immutable -- a questionable design
decision (see #1261), which already generated quite some additional complexities.
In the course of this »exercise«, I could again clarify that the implementation
of perfect forwarding works as expected on modern compilers — confusion may arrise
sometimes due to ''copy elision'' (which the compiler is required to perform
since C++17, even when the elided constructor has observable side effects).
And it can be derailed when (as was the case here) a »grab everything« constructor
accidentally ends up generating a copy- or move-constructor for the container class
itself. This is an instance of the problem documented with #963 ...
.... and the best solution is to abide by the rule-of-five (and a half)
and to put that `ReplacableItem` to where it belongs...
Ichthyostega
bc6a219543