Copy Constructor DIP and implementation

[Meta]

On Tuesday, 11 September 2018 at 15:08:33 UTC, RazvanN wrote:
> Hello everyone,
>
> I have finished writing the last details of the copy 
> constructor DIP[1] and also I have published the first 
> implementation [2]. As I wrongfully made a PR for the DIP queue 
> in the early stages of the development of the DIP, I want to 
> announce this way that the DIP is ready for the draft review 
> now. Those who are familiar with the compiler, please take a 
> look at the implementation and help me improve it!
>
> Thanks,
> RazvanN
>
> [1] https://github.com/dlang/DIPs/pull/129
> [2] https://github.com/dlang/dmd/pull/8688

If @implicit is the contentious part of this DIP, maybe it would 
be a good idea for us to instead use a `pragma(copyCtor)` or the 
like to avoid having to add another attribute while preserving 
backward-compatibility. Like @implicit, it's very easy to turn 
existing constructors into copy constructors just by adding the 
pragma, and they can be added to code with impunity because even 
older versions of the compiler will just ignore pragmas they 
don't recognize.