[boost] [units] problems

Subject: [boost] [units] problems
From: Robert Ramey (ramey_at_[hidden])
Date: 2013-09-13 16:54:48

I want and need the boost.units functionality.  I'm sure that this is what I 
want.  But I've spend a lot of time going through the documentation and I'm 
having real difficulties figure out how to use this.  There's  a lot there 
so I feel that what I want must be in there somewhere.  I've started going 
through the tutorial example and there are a couple of problems.  First of 
all, it doesn't compile on my machine.  Looking at the tutorial, it actually 
contains two programs - one of which is commented out.  I tried the 
commented out one as well - it didn't compile either. Note that other than 
in the header, there are very few if any comments in this code.  It doesn't 
qualify as a tutorial.

What I expect to see is:

#include <boost/units/quantity.hpp>
#include <boost/units/systems/si/length.hpp>
#include <boost/units/base_units/us/mile.hpp>
void main(){
    using namespace boost::units;
    using namespace boost::units::si;
    using namespace boost::units::us;
    quantity<length, float> l1;
    l1 = 1000.0 * meters;
    quantity<length, float> l2;
    l2 = 1.0 * miles; // compile error
    quantity<length, float> l3 = l1 + l2;
}

and I expect this to pretty much work.  The documentation says " Implicit 
conversions between unit systems are allowed only when the reduced units are 
identical, allowing, for example, trivial conversions between equivalent 
units in different systems (such as SI seconds and CGS seconds)" so I 
expected that it can convert miles into kilometers.  This is a 
disappointment - but I'll assume that the authors have a good reason for 
this.

So I'm interest in figuring out how to fix this but the manual doesn't seem 
to help me.  I know a huge amount of effort has been invested in this 
package, but I'm afraid this issue of documentation is a big obstacle to 
this package being used every where it could be.

Note to authors of boost libraries.  When you think you've got the 
documentation done, hand it to someone who isn't familiar with it and ask 
him to make a small example using the library in 30 minutes.  If he can't do 
that, it's time to go back to work.  Most users will give up if they can't 
get some sort of love back from the library in that amount of time.

Robert Ramey