using System;

​

public class Program

{

    public static void Main()

    {

        A a = new A(0.0d);

        B b = new B(0.0d);

        // this will error

        A result = a + b;

    }

}

​

public struct A

{

    private readonly double value;

    public A(double value)

    {

        this.value = value;

    }

​

    // just comment it out

    /*

    public static A operator +(A a, B b)

    {

        throw new InvalidOperationException();

    }

    */

    public static implicit operator A(double value)

    {

        return new A(value);

    }

}

​

public struct B

{

    private readonly double value;

    public B(double value)

    {

        this.value = value;

    }

​

    public static implicit operator B(double value)

    {

        return new B(value);

    }

}