Implicit (bool) and == operator override - handle if statements correctly

Question

I have a custom class with implement both the == and the implicit for boolean operator.

Is this the correct way to handle all possible, if ==/!= statements and get the expected result? Like this:

public class Foo
{
    public bool Result { get; set; }

    public static bool operator ==(bool @bool, Foo foo)
    {
        return Equals(foo, @bool);
    }
    public static bool operator !=(bool @bool, Foo foo)
    {
        return NotEquals(foo, @bool);
    }
    public static bool operator ==(Foo foo, bool @bool)
    {
        return Equals(foo, @bool);
    }
    public static bool operator !=(Foo foo, bool @bool)
    {
        return NotEquals(foo, @bool);
    }
    public static bool operator ==(Foo foo, Foo fooB)
    {
        return Equals(foo, fooB);
    }
    public static bool operator !=(Foo foo, Foo fooB)
    {
        return NotEquals(foo, fooB);
    }
    public static implicit operator bool(Foo foo)
    {
        try { return foo.Result; }
        catch { return false; }
    }

    private static bool Equals(Foo foo, Foo fooB)
    {
        if (object.Equals(foo, null))
        {
            if (object.Equals(fooB, null))
                return true;

            return false;
        }

        if (object.Equals(fooB, null))
            return false;

        return foo.Result == fooB.Result;
    }
    private static bool NotEquals(Foo foo, Foo fooB)
    {
        if (object.Equals(foo, null))
        {
            if (object.Equals(fooB, null))
                return false;

            return true;
        }

        if (object.Equals(fooB, null))
            return true;

        return fooB.Result != foo.Result;
    }
    private static bool Equals(Foo foo, bool @bool)
    {
        if (object.Equals(foo, null))
            return true;

        return @bool == foo.Result;
    }
    private static bool NotEquals(Foo foo, bool @bool)
    {
        if (object.Equals(foo, null))
            return false;

        return @bool != foo.Result;
    }

}

I am especially wondering about the fact that its seems you really need to implement overloads for either

if (new Foo() != true)

and

if (true != new Foo())

Answer 1

I think you've written too much code :-)

The following is sufficient:

public class Foo
{
    public bool Result { get; set; }

    public static implicit operator bool(Foo foo)
    {
        return !object.ReferenceEquals(foo, null) && foo.Result;
    }
}

The compiler will then know how to implicitly convert variables of type Foo into bool. (And null will be converted to false).

So, when you write:

new Foo() == false

The compiler will use the implicit type converter to get a bool value from Foo and then use the standard equality operator for bool.

If we look at the IL that the compiler generates for that expression we find:

newobj instance void FooBool.Foo::.ctor()               // new Foo()
call bool FooBool.Foo::op_Implicit(class FooBool.Foo)   // implicit operator (Foo => bool)
ldc.i4.0                                                // false
ceq                                                     // equality operator (bool)

Here's a test:

static void Main(string[] args)
{
    AssertTrue(new Foo() == false);
    AssertTrue(false == new Foo());
    AssertFalse(new Foo() != false);
    AssertFalse(false != new Foo());
    AssertTrue(new Foo { Result = true } == true);
    AssertTrue(true == new Foo { Result = true });
    AssertFalse(new Foo { Result = true } != true);
    AssertFalse(true != new Foo { Result = true });
}

static void AssertTrue(bool value)
{
    Console.WriteLine(value ? "ok" : "not ok");
}

static void AssertFalse(bool value)
{
    Console.WriteLine(value ? "not ok" : "ok");
}

It prints ok for each test. So this simplified code should fulfill your needs if I understood them correctly.

UPDATE

To allow the equality operator to work for instances of Foo (which may be null):

public static bool operator ==(Foo a, Foo b)
{
    if (object.ReferenceEquals(a, b))
    {
        return true;
    }
    else if (object.ReferenceEquals(a, null))
    {
        return !b.Result;
    }
    else if (object.ReferenceEquals(b, null))
    {
        return !a.Result;
    }
    else
    {
        return a.Result == b.Result;
    }
}

You should then also implement the inequality operator:

public static bool operator !=(Foo a, Foo b)
{
    return !(a == b);
}

And also override GetHashCode + Equals

public override int GetHashCode()
{
    return this.Result ? 1 : 0;
}

public override bool Equals(object obj)
{
    if (object.ReferenceEquals(obj, null))
    {
        return !this.Result;
    }

    Type t = obj.GetType();

    if (t == typeof(Foo))
    {
        return this.Result == ((Foo)obj).Result;
    }
    else if (t == typeof(bool))
    {
        return this.Result == (bool)obj;
    }
    else
    {
        return false;
    }
}