Re: Is there a way to make a class variable visible but constant to outsiders, but changeable (mutable) to the class itself?

[Meta via Digitalmars-d-learn]

On Tuesday, 24 May 2016 at 15:07:55 UTC, Jonathan M Davis wrote:
On Tuesday, May 24, 2016 10:10:16 Steven Schveighoffer via 
Digitalmars-d-learn wrote:
A while ago, I discovered that this works.
class C {
    union
    {
       private int _my_var;
       public const int my_var;
    }
    void do_something() { _my_var = 4; }
}

Yeah. That's basically what Rebindable does, though in its 
case, it's not really allowing you to mutate any data, just 
what the reference refers to. Regardless, it does seem like a 
hole in the type system.

- Jonathan M Davis

I don't believe so. H. S. Teoh recently fixed a definite bug when 
you have something like:

struct S
{
    union
    {
        int n1;
        immutable int n2;
    }
}

But I'm pretty sure the case where n2 is const was purposely not 
fixed as it doesn't break the type system. The value of a const 
variable can be changed at any time out from under you, so a 
union of a mutable and const int does not break any type system 
guarantees.