class opBinary overloading. value + null and null + value

[ref2401]

On Sunday, 21 October 2012 at 20:42:08 UTC, cal wrote:
> On Sunday, 21 October 2012 at 20:34:51 UTC, ref2401 wrote:
>> what should i do to make my binary operation commutative?
>
> You can overload opBinaryRight:
>
> MyClass opBinaryRight(string op: "+")(MyClass rhs)
> {
>    if (rhs is null)
>    {
>      return null;
>    }
>    MyClass result = new MyClass(value + rhs.value);
>    return result;
> }
>
> http://dlang.org/operatoroverloading.html

in the following case

auto v5 = v1 + v2;

there will be compile time error:
overloads pure @safe MyClass(MyClass rhs) and pure @safe 
MyClass(MyClass lhs) both match argument list for opBinary