Read-only property without @property

[Daniel N 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

Thanks, I love this!

There is actually a very important ABI difference, in all other 
"property" implementations in other languages(of which I'm 
aware), the ABI is changed to be a method rather than a member, 
for this reason I think we shouldn't refer to this feature as a 
"property", maybe "field/member" is more appropriate?

Both properties and "access restricted fields" has their place 
depending on what one is trying to accomplish, but in most cases 
I find myself wanting this very feature and not normal properties.

I couldn't resist trying this in C++, clang rejected it outright, 
GCC let it through with a warning.