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

From: Martin (adrianm_at_[hidden])
Date: 2005-01-09 05:13:35

> In our applications, we can't predict the currency of a money variable 
> at compile-time, and the overhead of the currencies is acceptable due to 
> the very lean implementation (only 4 bytes, single comparison for checks).

Yes, that was one of the reasons I removed the currencyid from the type but I 
didn't find any good way to specify the currency for individual objects.

Do you have it as a constructor argument or is it a property?

> The basic_decimal<T>-class is just a generic float point interface. It 
> defines what can be done, not how it's done. Example: Depending on T, 
> some classes have member functions where others have free functions. 
> It's round(x,2) vs. x.round(2).

Sorry but I don't understand what you gain from that approach. If I understand 
correctly you will need a specialization of basic_decimal for each type T. A 
specialization has no correlation to the template (except the name) so you 
will not get any compile errors if the specialization basic_decimal<double> 
has a completly different interface than basic_decimal<int>.

> syntax. Actually, I have a decimal_traits<T>-class which is specialized 
> for all T's that can be used in our applications with basic_decimal and 
> basic_money.

Ok, basic_decimal only forwards calls to the decimal_traits but that still 
doesn't change the fact that you need specializations for each type.

Why is it better to have decimal_traits<decimal64> & 
decimal_traits<decimalBCD> than to implement decimal64 & decimalBCD to have 
the same interface? 
I can understand it if there are some types that don't need specialization of 
decimal_traits. Writing basic_money<double> is very confusing to me since it 
gives me no hint on what I get. If I write basic_money<decimalDouble> I 
understand that I can look in the documentation for deicmalDouble.

> Only if decimal64 and decimalBCD have the same interface. And you can't 
> replace it with double or RWDecimal<RWMP3Int>, because their interfaces 
> differ.

In your implementation decimal_traits<decimal64> and 
decimal_traits<decimalBCD> need to have the same interface so what's the 
difference.

Don't get me wrong here. I am usually in favour of traits classes but in this 
case I don't see the point.

Going forward.

Can we combine our work? I like your run-time currency and maybe you can 
convince me about the traits but I assume your solution is part of your work 
so it can't be used in boost.