It would be useful for this purpose to provide an ability to iterate through the values or ability to pass a visitor or both. IOW, very long and hard to read lines. I would welcome some way to fill in the exception in more compact form. I, however, do not have any suggestion how to do it. 4. I would like the ability to collect traces generated by what() function
I've been playing around with Exception tonight and have a variation with the following changes: 1. A more concise throw statement is desirable. In the variation, both tagged and untagged fields can be added. The order of the fields is preserved, using a linked list, instead of a map. Formatting of the "what string" is still delayed until exception::what is called. The bare minimum the amount of code needed to throw an exception with a message that contains both a useful message for debugging and marked fields for reporting back to the user. throw exception() << "The frobknob is out of range: its value is " << error_info<value_tag>(value)<< " but the maximum value is " << max; 2. The potential for a null return value from get_error_info is going to cause bugs. In this variation, this potential is eliminated by using a visitor. A visitor can be applied to the fields to manipulate individual values. The visitor is applied to each field with a matching type. The field need not be tagged in order to be visited. catch(exception&e) { using lambda; int x(0); e.visit(on_error_info(value_tag(),var(x)=_1)); cerr << "frobknob value is " << x << "\n"; int y(0); e.visit(on_error_info<int>(var(y)=_1)); cerr << "max was " << y << "\n"; } 3. Sometimes you really want to throw a different exception type that better describes the context of the error. In this case, the list of fields from one exception can be added to a second exception. This affects both exception::what and exception::visit. catch(exception&e) { throw can_not_load_file() << "could not open " << error_info<filename_tag>(filename) << " because " << e; } Source code is here http://joshuanapoli.com/exception -Joshua