Re: [boost] units: review

From: Lewis Hyatt (lhyatt_at_[hidden])
Date: 2007-03-29 15:17:30

Matthias Schabel wrote:
>> While quantity_reinterpret_cast may not be perfectly analogous to
>> reinterpret_cast, it represents the reinterpretation of a raw number
>> as being of a different type, and so I think it's a pretty good name.
>> Just as importantly, I can't think of anything better.  Do you have
>> any other ideas?  quantity_unsafe_cast? quantity_arbitrary_cast? :)
> 
> Sorry, I think I muddied the waters here - I agree that  
> quantity_reinterpret_cast should be reserved for those cases where  
> access to the raw data is necessary. I was just saying that we can  
> write things like
> 
> quantity<SI::length,double>	q;
> quantity<SI::length,int>		r;
> quantity<CGS::length,double> s;
> quantity<CGS::length,int>		t;
> 
> q = quantity<SI::length,double>(r);
> q = quantity<SI::length,double>(s);
> q = quantity<SI::length,double>(t);
> 
> already, so the only non-degenerate use case of quantity_cast is to  
> take a raw value and return a quantity:
> 
> q = quantity_cast< quantity<SI::length,double> >(1.5);

I think you are right that quantity_cast becomes unnecessary, and in the 
last usage there, the user should have to specify the units or use 
quantity_reinterpret_cast.

One more thought, instead of:

        q = quantity<SI::length,double>(r);

what about a syntax like
        
        q.convert_from(r)

to emphasize that this is performing a safe unit conversion, and to 
avoid having to repeat the type name?

-lewis