Read-only property without @property

[John Colvin via Digitalmars-d]

On Friday, 26 September 2014 at 19:47:15 UTC, Steven 
Schveighoffer wrote:
> I wanted to bring this over from D.learn, because I've never 
> seen this before, and it's an interesting solution to creating 
> a property without much boilerplate.
>
> So here it is:
>
> class Foo
> {
>    union
>    {
>       private int _a; // accessible only in this module
>       public const int a; // accessible from anywhere, but read 
> only
>    }
> }
>
> And it works now, probably has for a while.
>
> Thoughts? This can easily be boilerplated in something like 
> roprop!(int, "a")
>
> I am really not sure what union does to compiler optimization 
> or runtime concerns, if it has any significant drawbacks. From 
> what I can tell, it's a valid solution.
>
> Credit to Mark Schütz for the idea.
>
> -Steve

I've often thought of such approaches, but not used them for fear 
of causing some horrible undefined behaviour (whether intentional 
or via a compiler bug). Are my fears misplaced?