Re: [boost] Re: Re: lexical_cast and gcc 2.96

From: Peter Dimov (pdimov_at_[hidden])
Date: 2001-10-18 07:28:54

From: "Kevlin Henney" <kevlin_at_[hidden]>
> >   From: "Peter Dimov" <pdimov_at_[hidden]>
> >
> >From: "Kevlin Henney" <kevlin_at_[hidden]>
> >> I think this is an excellent suggestion. What are Booster preferences
> >> from the following possibilities:
> >>
> >> (1) Add specific throws:
> >>   (a) Not at all.
> >>   (b) Distinguished by initialiser string.
> >>   (c) Distinguished by enum.
> >>   (d) Both (b) and (c).
> >
> >I strongly suggest
> >
> >(e) distinguished by exception type.
>
> I should have mentioned why I didn't include this option: historically
> the original numeric_cast had multiple exception types, but there was a
> feeling that this was superfluous. I was assuming that the same would
> also apply to lexical_cast, for consistency. However, I think that now
> that you have suggested it, it ought to be up for consideration.

Perhaps I need to elaborate. :-)

Distinguishing different exceptions by type, rather than by enum, allows
clients to pick their own subset of exceptions that they are interested
with. If this weren't important, lexical_cast would simply throw
std::bad_cast.

In a real world application, I'll use both the initializer string (it's in
English, usually not suitable for the end user) for debug, log, auto bug
report purposes _and_ the exception type to present an appropriate error
description to the end user.

Depending on the application (and the user) I may decide to only catch
std::bad_cast and display a generic error message, or I may catch the
individual errors and display a message that is somehow tied to the error.

I hope this makes sense. :-)

It's true that individual exception types make the library code rather
verbose but I haven't found a better error handling solution.

For example, my I/O library defines:

class exception: public std::exception;
class logic_error: public exception;
class file_error: public exception;
class open_error: public file_error;
class read_error: public file_error;
class eof_error: public read_error;
class write_error: public file_error;
class seek_error: public file_error;
class compression_error: public exception;
class decompression_error: public exception;
class invalid_format: public exception;
class invalid_signature: public invalid_format;
class invalid_version: public invalid_format;
class invalid_count: public invalid_format;

In 'toy' programs (command line utilities) I never catch anything other than
io::exception.

--
Peter Dimov
Multi Media Ltd.
PS: string specializations? wstring specializations?