why can't I call const methods on shared objects?

[FreeSlave via Digitalmars-d-learn]

On Sunday, 11 May 2014 at 07:31:10 UTC, FreeSlave wrote:
> On Friday, 9 May 2014 at 21:42:14 UTC, Vlad Levenfeld wrote:
>> Is this still the case if the method is const or pure?
>
> Const methods still require synchronization, because other 
> threads may change some data, needed by const method while 
> method is executed, and then you may get wrong results.
>
> Consider:
>
> class Point
> {
> public:
>     float x;
>     float y;
>
>
> }

I send before I end(

class Point
{
public:
     float x;
     float y;

     Tuple!(float, float) getLengthAndAngle() const
     {
         float l = sqrt(x*x+y*y);
         //other thread change x or y
         float a = atan2(x, y);
         return tuple(l, a);
     }
}