Generic operator overloading for immutable types?

[Gary Willoughby via Digitalmars-d-learn]

In the following code is there any way to make the `opBinary` 
method generic to be able to accept immutable as well as a 
standard type? The code currently passes the unit test but I 
wonder if I could get rid of the duplication to overload the 
operator? I'm failing badly.


import std.stdio;

struct Rational
{
	public long numerator;
	public long denominator;

	public immutable Rational opBinary(string op)(immutable Rational 
rhs)
	{
		static if (op == "+")
		{
			return Rational(0, 0);
		}
		else
		{
			static assert(0, "Operator '" ~ op ~ "' not implemented");
		}
	}

	public Rational opBinary(string op)(Rational rhs)
	{
		static if (op == "+")
		{
			return Rational(0, 0);
		}
		else
		{
			static assert(0, "Operator '" ~ op ~ "' not implemented");
		}
	}
}

unittest
{
	auto foo = Rational(1, 3);
	auto bar = Rational(1, 6);
	writefln("%s", foo + bar);

	auto baz = immutable Rational(1, 3);
	auto qux = immutable Rational(1, 6);
	writefln("%s", baz + qux);
}