AMDG On 11/25/2011 05:11 AM, Janek Kozicki wrote:
(***) it seems strange that I need to take .value() here. The result is dimensionless, why can't it directly convert to complex<double> ? There is a risk that .value() would be expressed in millimeters or angstroms or whatever (maybe depending on dd), and then .value() would return a wrongly scaled number?
This is an idiosyncrasy of overload resolution. std::complex::operator+= is a template, so an implicit conversion doesn't work. The template argument can't be deduced.
OK. So I have to use .value().
The question here: should I expect here some scaling problems? For example:
a = 1nm b = 1km c = (a/b).value()
Will c become 1.0, with units scaling being lost, due to directly taking .value() without taking care of unit scaling. Or would it be correctly 1e-12 ?
It will be 1.0. in this case. To be safe use static_cast, or boost::implicit_cast.
In my problem I am calculating exponent then multiply and divide by length. In fact the exponent argument is supposed to be dimensionless also! And as you see I multiply wavenumber by length. I assume the conversions to ::one are good here :)
Another question:
complex<double> i(0,1); quantity<wavenumber,complex<double> > k=2*pi/lambda; // [....] a += (dd*exp(i*k*r)/r).value();
do I really need to define wavenumber k as being complex? After all it's multiplied by 'i' so it should get converted automatically?
It's the same problem as above with int/double.
quantity<length> wavelength ( 632.8 *nano*meters); quantity<length> wavelength = 632.8 *nano*meters; This isn't assignment. It's copy construction and requires an implicit conversion which is forbidden.
why it is forbidden? I think it would be more convenient to allow this.
In general, any conversion that causes the underlying value to change is explicit. In Christ, Steven Watanabe