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From: Steven Watanabe (steven_at_[hidden])
Date: 2007-03-28 15:27:55


Noah Roberts <roberts.noah <at>> writes:

> <snip>
> In my case I was thinking a unit
> type that exists solely for providing conversions. Not always is that a
> multiplication.
> <snip>

Ok. Good point. You can use type erasure to get this effect
and be able to use the static conversions at runtime.

template<class Quantity, class InputQuantity>
Quantity quantity_converter(const typename Quantity::value_type& v) {

> Also, your idea has problems when you account for rounding. Rounding is
> often done before you display data to a user. In cases when this data
> can come from a calculation or from the user it is hard to decide when
> to round and when not. If you apply rounding and conversions on both
> input and output and add rounding into the mix you can have a user
> entered value that gets reported back to the user as something else.
> This is not acceptable in many cases.

I may be wrong, but in order to avoid any excess loss
of precision you have to store a set of all the base
units and track the actual unit at runtime involving
a merge with every multiplyor divide. This kind of
overhead is not always acceptable.

> At any rate, there are ways to solve the whole thing regardless. The
> question is, what is the use of a library that only does static
> conversions.

As has been stated many times conversions are not
the primary point of the library.

> How often is one going to use multiple "systems"?

Hopefully not very often.

In Christ,
Steven Watanabe

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