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.
This is an object lesson in why using the value() method should be a last resort. I do think that we should try to get sensible behavior, without too many contortions, with the various built in types. A slight tangent : I'm thinking that we are going to need to revisit scaled units now that std::ratio exists and takes over the prefixes. Steven, any sense of how difficult it will be to replace our static_rational with std::ratio? I took a quick look and it doesn't look like a disaster - hoping there are no subtle gotchas... I guess we will have to overload operator*(std::ratio<N,D>,unit<S>)? This problem arose when I tried to compile Janek's code with Xcode 4.2 using C++11 mode... <ratio> must be pulled in by default, though not sure why.
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
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