Re: [boost] 5 Observations - My experience with the boost libraries

Subject: Re: [boost] 5 Observations - My experience with the boost libraries
From: Nicholas Howe (nicholas.howe_at_[hidden])
Date: 2010-03-28 13:38:46

On Thu, Mar 25, 2010 at 6:58 PM, Tom Brinkman <reportbase2007_at_[hidden]>wrote:

> 1) Boost uses exceptions.
>

I'm a game programmer.  I've worked at companies that disable exceptions.
 One advantage of exceptions is that when they occur, the stack is unwound
and object destructors are executed.  Another is that higher-level code is
given an opportunity to recover from the exceptional condition.  If you
don't care about either of these things, it might be acceptable for your
program to terminate at any point where it would normally throw an
exception.  Assuming your C++ implementation already terminates execution or
otherwise behaves acceptably when features like std::operator new
and reference dynamic_cast fail with exceptions disabled, I think you could
achieve that with Boost using the preprocessor as shown below.

#ifndef THROW_H
#define THROW_H

#include <cstdlib>

struct Throw
{
};

template< class T >
inline void operator <<( Throw &, T const & )
{
std::exit( EXIT_FAILURE );
}

#define throw Throw() <<

#endif

You would include "Throw.h" before any headers that throw exceptions,
perhaps using a compiler's force-include feature.  You could compile the
non-header-only Boost libraries with this, too.  You could overload operator
<< to do different things with different exceptions, such as reporting the
error in some fashion, or using platform specific code to detect if a
debugger is attached and break if so.  This would also have the advantage
that it would to some extent allow your C++ programmers to use exception
semantics in their own code.

If you come across cases where you don't want to terminate, and you're very
clever and lucky, you might be able to make operator << translate the
exception into a return value for the function.  This would be difficult
because the same exception could be thrown by functions with different
return value types.  You could return a Throw & from operator << and add
conversion operators to Throw to make it turn into whatever the function
wants.  However, it would be difficult to know what an appropriate return
value would be.

I think this simple header could allow Boost to be used in an environment
that frowns on exceptions without any changes to Boost.  Of course, I
haven't tried any of it.
Nick