Copy Constructor DIP and implementation

[Jonathan M Davis]

On Monday, September 24, 2018 10:44:01 AM MDT Meta via Digitalmars-d-
announce wrote:
> On Sunday, 23 September 2018 at 01:08:50 UTC, Jonathan M Davis
>
> wrote:
> > @implicit is just there because of the fear of breaking a
> > theoretical piece of code that's going to be extremely rare if
> > it exists at all and in most cases would continue to work just
> > fine even if it did exist.
> >
> > - Jonathan M Davis
>
> I somewhat agree with this argument, but overall I hate this
> attitude of "we should just make the change because it *probably*
> won't break any code", and then bonus points for "code that does
> this is wrong anyway so we shouldn't care if we break it". I've
> already been burned by that a couple times using D, and I imagine
> heavy corporate users with large code bases have many more
> problems with this.

In this particular case, a transitional compiler flag like we've done with
other DIPs makes _far_ more sense than forcing everyone to use an attribute
forever - especially when forgetting to use the attribute is going to be a
further source of bugs, one which would _easily_ outweigh any code breakage
caused by not having the attribute. But having a transitional compiler flag
would give us a way to deal with the potential code breakage if it exists.

- Jonathan M Davis