move semantics are a mess

[Per Nordlöw]

On Sunday, 26 May 2019 at 18:24:17 UTC, Manu wrote:
> I've been trying to do some initial work with copy ctor's, and 
> that has lead me to closely scritinise the various construction 
> flow's, and it's revealed a whole bunch of issues with move 
> semantics.

A cumbersome but working way of experimenting with the potential 
(performance) benefits of eliding copy construction of the 
elements in `args` would be to replace

void emplaceRef(UT, Args...)(ref UT chunk, auto ref Args args)
if (is(UT == core.internal.traits.Unqual!UT))
{
     emplaceRef!(UT, UT)(chunk, args);
}

with

void emplaceRef(UT, Args...)(ref UT chunk, auto ref Args args)
if (is(UT == core.internal.traits.Unqual!UT))
{
     static if (args.length == 1)
     {
         emplaceRef!(UT, UT)(chunk, move(args[0]));
     }
     else static if (args.length == 2)
     {
         emplaceRef!(UT, UT)(chunk, move(args[0]), move(args[1]));
     }
     else ...up to args.length
}

and similarly for the calls to

     p.__ctor(args)

in

void emplaceRef(T, UT, Args...)(ref UT chunk, auto ref Args args)

.