[boost] Re: Any interest in a decimal and money class?

From: Martin (adrianm_at_[hidden])
Date: 2005-01-08 16:22:39

Daniel Frey <d.frey <at> gmx.de> writes:

> 
> I strongly suggest to use a currency, as otherwise you'll likely miss 
> the intended audience's requirements.

I actually had this implemented at start but removed it at one point. I 
implemented it like this:

template <class DecimalT, int CurrencyId = 0>
class money_base ...

You created different currencies by doing
typedef money_base<decimal64, 1> USD;
typedef money_base<decimal64, 2> EUR;

If I needed values without currency I just used the decimal type.
decimal exchangerate(usd.as_decimal(5) / eur.as_decimal(), 5); // 5 decimals

(Your debtor example would probably need to use boost.any with my solution)

Your run-time currency type is an interesting approach.

> > Integers works as both money and decimal so Money*2 and Money+1 is always 
> > allowed.
> 
> money*int is OK, money+int is not. And FWIW, I never saw any of my 
> colleagues complain about money+int not compiling. If the compiler 
> happens to catch it, it usually means that it saved them from a having bug!

And I was afraid my interface was to strict. Thanks.

> The application can/should then create central typedefs:
> 
> typedef basic_decimal<long double> decimal;
> typedef basic_money<decimal::value_type> money;

Not sure I understand. The implementation of decimal arithmetic will be very 
different depending on the type (e.g. double, int, BCD strings) so I don't see 
how it can all fit into a basic_decimal. It is fine as an ABC but does it 
really add anything (except virtual calls).

Also shouldn't basic_money use the decimal type instead of the decimal type's 
internal representation (i.e. basic_money<decimal>)

> That way, you can switch your complete application for different 
> underlying types that are used for the real calculations easily.

You can do the same with my solution but it would look like this:

  typedef money_base<decimal64> money;
or
  typedef money_base<decimalBCD> money;

typedef money::decimal_type decimal;