getting rid of immutable (or const)

[berni via Digitalmars-d-learn]

I still struggle with the concept of immutable and const:
import std.stdio;

void main()
{
    auto p = Point(3);
    auto q = p.x;
    writeln(typeof(q).stringof);
}

struct Point
{
    @property immutable long x;
}

The type of q is immutable(long). But I need a mutable q. I found 
two ways:

a) long q = p.x;
b) auto q = cast(long)p.x;

Either way I've to specify the type "long" which I dislike (here 
it's not a real burdon, but with more complicated types it might 
be). Is there a way, to make q mutable without having to write 
the type explicitly?