Rob Stewart wrote:
From: Martin <adrianm@touchdown.se>
Your decimal64 is both an interface *and* an implementation. I just suggest to separate it. Let basic_decimal take care of the interface, while decimal64 takes care of the implementation.
I can agree that the interface could be formally specified as a basic_decimal but still don't understand the benefits of a decimal_traits vs a class that implements the basic_decimal interface.
OK, ask Roguewave to modify their classes to implement the basic_decimal interface. They won't do that, right? So what will you do now? Write a wrapper? OK, but what is the easiest way to write a wrapper? I don't want to limit the T's to types that conform to my interface. So I need wrappers. So, IMHO, the question is how to make it safe and easy to create such wrappers (or adaptors)?
basic_decimal can utilize fundamental operations from the traits class to provide the full interface. Put another way, the traits class needn't provide the entire interface that basic_decimal provides, so adapting a new type to fulfill the basic_decimal interface is easier. (That's theoretical, of course. I haven't any idea how much logic Daniel's basic_decimal implements beyond that provided by his traits class.)
I think this is generally correct, although there were more reasons for a basic_decimal class. It allows me to control the interactions with basic_money. I can declare operators like this: template< typename T > basic_money<T> operator*(basic_money<T> lhs, basic_decimal<T> rhs) which is better than allowing basic_money<T> * T because I know more about basic_decimal<T> than about T. Maybe this is influenced by the bad design of some T's, but that's the real world. :( So this argument for basic_decimal<T> might also be seen as nannyism, but to me, basic_money and basic_decimal belong together because it's the only way I can make basic_money safe. having a decimal_traits class and writing mappings to some type T is a consequence. And having written basic_decimal<T> myself, I know exactly all ctors, conversions, etc. provided, no chance for T to create a SNAFU but adding a ctor which takes a double or something stupid like that. The decimal_traits are not only a helper to write a mapper to some T faster, they also help to make it safer, because their interface is more explicit and more restricted than that of a generally useful interface of some T. Regards, Daniel