Support for Complex QuantityValue

[mwagnerEE]

Have you ever considered implementing the System.Numerics.Complex data type? Instead of some quantities using decimal and some using double, could they not all use QuantityValue? And in that event, what would prevent the extension of this struct to have a third field to store Complex as like this:

private QuantityValue(Complex val)
{
    _valueComplex = val;
    _valueDecimal = null;
    _value = null;
}

#region To QuantityValue
/// <summary>Implicit cast from <see cref="Complex"/> to <see cref="QuantityValue"/>.</summary>
public static implicit operator QuantityValue(Complex val) => new QuantityValue(val); // Complex
#endregion

#region To Complex

/// <summary>Explicit cast from <see cref="QuantityValue"/> to <see cref="Complex"/>.</summary>
public static explicit operator Complex(QuantityValue number)
{
    return number._valueComplex ?? new Complex(number._value ?? (double)number._valueDecimal.GetValueOrDefault(), 0);
}

#endregion

/// <summary>Returns the string representation of the numeric value.</summary>
public override string ToString()
{
    if (_value.HasValue)
    {
        return _value.ToString();
    }
    else if (_valueDecimal.HasValue)
    {
        return _valueDecimal.ToString();
    }
    else if (_valueComplex.HasValue)
    {
        return _valueComplex.ToString();
    }
    else
    {
        return "0";
        //throw new System.Exception();
    }
}

[angularsen]

Hi, Complex type has not been discussed before. Do you have any examples of using complex numbers to represent a quantity value? Would you use it if it was implemented?

As for using QuantityValue as the internal value, maybe. I haven't really thought about it, but maybe there is some merit to it. I'm trying to come up with counter-arguments not to do so, and I think the best I can think of right now is that serialization will be more complicated and it probably adds some extra bytes for memory sensitive applications.

[mwagnerEE]

I'm an EE and I'm trying to make a power flow analyzer. Complex values are used all the time in Electrical. In messing around with allowing arbitrary arithmetic of quantities, I did implement Complex values. Although I replaced decimal and double for ease of prototyping. I ended up just copying DotNet's Complex and extending it. It probably would take up more space but is otherwise hidden in that a double is implicitly convertible to Complex so if you didn't use the imaginary parts you could continue to use doubles

[angularsen]

Related: #1084

I don't think Complex fits into that solution though, we would probably have to extend QuantityValue somehow to make it work. That would probably also ramp up the byte size again and I would like to avoid that.

At this point, it feels like Complex values may be out of scope for UnitsNet. If you see a clever way forward I'm open to it, but it may simply be better solved outside.