Re: simple class
Richard Damon <Richard@Damon-Family.org> writes:
If we started with a
typedef double MoneyType;
at the beginning of the header, and getBalance() defined to return a
MoneyType, then if the client used the MoneyType also, then no change in
client code might be needed.
In the client, one can have case A (old solution):
double b = account.getBalance();
or case B (your new suggestion):
MoneyType b = account.getBalance();
. In case A, the client's author can then write
::std:cout << 0.05 * b;
. In case B, the client needs more support from the
implementation to be able to do this. The client's author is
not supposed to know that ?MoneyType? is just ?double?.
Therefore, he cannot write:
::std:cout << 0.05 * b;
, because he does not know whether MoneyType supports those
operations and what their semantics is. But usually the
client might need to calculated something with the balance
or to serialize it to a human-readable stream. So he needs
more support from the library than just the statement
?MoneyType is an opaque type that you do not need to know
anything about.?
Possibly, MoneyType might grow to become a new type
implemented by a class. Well, then this class better not
have a ?toDouble()? method, because otherwise the clients
might use it and then the same problem will arise anew.