Re: [boost] Units of data

Subject: Re: [boost] Units of data
From: Matthias Schabel (boost_at_[hidden])
Date: 2009-07-02 15:07:28

> void foo()
> {
> 	using boost::units::quantity;
> 	using namespace boost::units::data_capacity;
>
>        //Both of these fail with the message that there is no
> conversion to the destination
>        //type because the construcor is explicit
> 	quantity<data_capacity> compressed_size = 1000 * bytes;
> 	quantity<data_capacity, int> compressed_size2 = 1000 * bytes;

Implicit conversion is not allowed, and default value type is double -  
try :

quantity<data_capacity>      compressed_size(1000.0*bytes);
quantity<data_capacity,int> compressed_size2(1000*bytes);

> 	//Succeeds but gives a horribly long warning about conversion from
> 'double' to 'const int'
> 	//at file 'boost/units/detail/conversion_impl.hpp(342)', reference to
> class template instantiation at
> 	//boost/units/quantity.hpp(182)
>       	quantity<data_capacity, int> compressed_size3(1000 * bytes);
> }

If I remember correctly, this stems from the use of double precision  
in the conversion code. I think it would be difficult to get rid of  
this - most computations involving unit conversions do not involve  
exact integer arithmetic...

Matthias