Rogier van Dalen wrote:
On Wed, 20 Oct 2004 23:05:08 +0300, Peter Dimov <pdimov@mmltd.net> wrote:
Rogier van Dalen wrote:
// The actual Unicode string template <class CodeUnits, class NormalisationForm, class ErrorChecking> class string
By using ErrorChecking as a template parameter, you are encoding it as part of the string type, but this is not necessary, because there is no difference between values of strings with different ErrorChecking policies (ErrorChecking does not change the invariant). You should just provide different member functions for the two ErrorChecking behaviors, or pass the ErrorChecking parameter to the member functions that require it.
I hadn't yet looked at it this way, but you are right from a theoretical point of view at least. To get more to practical matters, what do you think this should do:
unicode::string s = ...; s += 0xDC01; // An isolated surrogate, which is nonsense
? Should it throw, or convert the isolated surrogate to U+FFFD REPLACEMENT CHARACTER (Unicode standard 4 Section 2.7), or something else?
Whatever is most common. My choice would probably be 'throw', but I haven't used Unicode strings enough to have a strong opinion.
And what should the member function with the opposite behaviour be called?
s.append( 0xDC01 ); // default (throw), += alias // pick your favorite from the list below s.append_and_correct( 0xDC01 ); s.append( 0xDC01, unicode::convert_on_error ); s.append<unicode::convert_on_error>( 0xDC01 ); I'd go with the first option based on general principles, all else being equal. There is also unicode::append_and_correct( s, 0xDC01 ); if the operation can be performed in "user space", i.e. doesn't need to be a friend of the string class. Or s += unicode::correct( 0xDC01 ); if the automatic correction does not depend on the left side.