Read-only property without @property

[Steven Schveighoffer via Digitalmars-d]

On 9/27/14 3:45 AM, Daniel Murphy wrote:
> "H. S. Teoh via Digitalmars-d"  wrote in message
> news:mailman.1799.1411796077.5783.digitalmars-d at puremagic.com...
>
>> Argh, looks like another incompletely-implemented part of the compiler:
>>
>> void fun() @safe {
>> union U {
>> int  p;
>> int* q;
>> }
>> U u;
>> u.p++; // compiles
>> u.q = null; // compiles
>> *u.q++; // x.d(9): Error: field U.q cannot be accessed in @safe code
>> because > it overlaps with a pointer

I think that this is equivalent to u.q++, since the ++ does not apply to 
the pointed-at variable, but at the pointer itself.

Weird, my tests showed that this was allowed.

More testing, I realize it's because it's a class variable.

This code compiles and runs:

class Foo
{
     union
     {
         int x;
         int *p;
     }

     void foo() @safe {*p = 5;}
}

void main() @safe
{
     auto f = new Foo;
     f.foo();
}

Which is similar to this code that does not:

void main() @safe
{
     union U {
         int x;
         int *p;
     }
     U u;
     *u.p = 5; // error
}

> Without unions, you can't create invalid pointers in @safe code.
> With unions, you can, but you can't access them.

The above shows you can in some situations, but I think that is a bug.

-Steve