Re: [Boost-users] boost::units units symbols/names

Subject: Re: [Boost-users] boost::units units symbols/names
From: Noah Roberts (roberts.noah_at_[hidden])
Date: 2011-07-26 16:29:56

On 7/26/2011 8:30 AM, Michael Powell wrote:
> Boost::units users,
>
> How do I get at the unit symbol or name? I think this type thing would
> be essential when receiving and parsing textual quantities from a client
> side application. So say I am given "1.0 in" or "2.3 m/s^2" and so on,
> and be able to translate that into the appropriate compile-time
> dimensional quantity.

Units are streamable and thus also can be lexical_cast.

template < typename Unit >
std::string label(Unit u) { return lexical_cast<std::string>(u); }

Being able to read them in the other way would be as simple as matching 
the unit you expect to the one you've gotten.  I can't think of any way 
to match some generic unit and return it since every unit is a different 
type.  You simply have to know what to expect with this library.

What you might be looking for here is a runtime unit system.  I devised 
such a system around the boost quantity system that somewhat works. 
Unfortunately I can't share it.  Basically I have a unit that does 
conversions, a quantity that stores a value, and these types convert 
to/from the boost versions of the same dimension before going into math 
functions.  All forms of I/O and user interaction are done in this 
wrapped thing and all formulas are done in a particular boost::units 
system.  It wasn't too difficult (except for some unfortunate things I 
was forced into--such as treating 3 different kinds of flow as the same 
variable).