throw specs on Standard destructors

[Benjamin Kosnik]

>#include <string>
>
>struct Base
>{
>  virtual ~Base() throw() {}
>};
>
>struct Der : Base
>{
>  std::string foo;
>};
>
>int main()
>{
>  Der d;
>}

Ouch.

>The problem here is that the default destructor for
>Der will have a throw spec which is the union of all
>bases and members.  Since std::basic_string has no
>throw spec, Der::~Der also will have none, which
>violates Base's destructor's spec.

%g++ simpson.cc
simpson.cc:9: looser throw specifier for `virtual Der::~Der()'
simpson.cc:5:   overriding `virtual Base::~Base() throw ()'
simpson.cc:9: looser throw specifier for `virtual Der::~Der()'
simpson.cc:5:   overriding `virtual Base::~Base() throw ()'
simpson.cc:9: looser throw specifier for `virtual Der::~Der()'
simpson.cc:5:   overriding `virtual Base::~Base() throw ()'

>My local work-around was to add the empty throw spec
>to basic_string, but I'm not clear if this is an
>ABI-breaking change, or if there is some other
>subtlety here.  I can't find the ABI FAQ for this.

Well, I've added it too, and then run 'make check-abi', which seem to
indicate that this is not an ABI breaking change, at least at the
exported symbol level.

15.4 - Exception specifications p12 also supports this.

As you've indicated, it would change the interface. I believe this is
explicitly allowd via

17.4.4.8 - Restrictions on exception handling p 3.

>I would assume the same should be done for auto_ptr.

Where would it stop? That part is unclear to me.

I think patches of this type are acceptable. Interested?

-benjamin