On 2/20/12 11:44 AM, foobar wrote:
This extra processing is orthogonal to the exception. the same exception
can be logged to a file, processed (per above example) and generate
graphical notification to the user, etc. The exception contains the
information pertaining only to what went wrong. the rest is not part of
this discussion.
Exactly. I don't see how a disagreement follows from here. So isn't it
reasonable to design the exception such that it can offer information
pertaining to what went wrong, in a uniform manner?
The exact same exception in the example would also be thrown on a
mistyped URL in an application that tries to scrape some info from a
website for further processing. The error is still the same - the url is
incorrect but different use cases handle it differently. In the former
example I might call to a i18n lib (someone already mentioned gettext)
while in the latter I'll call a logging library with the the mistyped
url (for statistics' sake).
in the first I use the url to find a closest match, in the second I want
to log said requested url. Both handled by *other* mechanisms.
in both cases the exception needs a url field and in both cases I have
no need for the Variant[string] map.
The Variant[string] map saves a lot of duplication whenever you want to
format a human-readable string (which is a common activity with
exceptions). It transforms this (I'm too lazy to write code anew by
hand, so I'll paste Jonathan's):
try
getopt(args, ...)
catch(MissingArgumentException mae)
{
stderr.writefln("%s is missing an argument", mae.flag);
return -1;
}
catch(InvalidArgumentException iae)
{
stderr.writelfln("%s is not a valid argument for %s. You must give
it a
%s.", mae.arg, mae.flag, mae.expectedType);
return -1;
}
catch(UnknownFlagException ufe)
{
stderr.writefln("%s is not a known flag.", ufe.ufe);
return -1;
}
catch(GetOptException goe)
{
stderr.writefln("There was an error with %s", goe.flag);
return -1;
}
//A delegate that you passed to getopt threw an exception.
catch(YourException ye)
{
//...
}
catch(Exception e)
{
stderr.writeln("An unexpected error occured.");
return -1;
}
into this:
try
getopt(args, ...)
catch(Exception e)
{
stderr.writeln(stringTemplate(typeid(e).toString(), e.info));
return -1;
}
The stringTemplate function loads the formatting template from a table
indexed on typeid(e).toString() and formats it with the info. It's
simple factorization.
Andrei
