enh rqst: warning about throw lists

[Andrew Marlow <apm35 at student dot open dot ac dot uk>]

I have an enhancement request for g++ to do with throw lists.
This enhancement is not to be default behaviour. It would
have to be enabled by some command line option.

When a function has a throw list (aka exception specification)
the compiler should check that the throw list is capable of
being honoured. If it might be violated then this gives a warning. In my
opinion this would make throw lists more useful like they are in Java.

Here's a example of code that has a throw list that cannot
be honoured (class E is an exception class):

class A
{
public:
    void doSomething()
    {
        // .....insert some code here
    };

    void doSomethingElse() throw(E)
    {
        doSomething();
    }
};

The above code is wrong because doSomethingElse() makes a
promise it might not be able to keep. And as we know, in
C++ the penalty for such a broken promise is death (via
unexpected->terminate).
We have said that doSomethingElse will only throw exceptions
of type E but it calls a routine that might throw any
exception, which will be propaged, violating the throw list.

Here is the code corrected:

class A
{
public:
    void doSomething()
    {
        // .....insert some code here
    };

    void doSomethingElse() throw(E)
    {
        try
        {
            doSomething();
        }
        catch(...)
        {
        }
    }
};

Now any exception is caught and suppressed. The throw list is honoured.

What do you think guys? I think that without a warning about possible
throw list violation, throw lists are next to useless. Especially when the
penalty for making a mistake is death. Maybe this is why ANSI themselves
do not use throw lists in standard library code that is defined to throw
exceptions under certain conditions.

Regards, 

Andrew Marlow.