kanze@gabi-soft.fr writes:

> As far as I can see, something like:
>
>     template< typename CharT >
>     std::basic_string< CharT >::const_reference
>     std::basic_string< CharT >::at() const
>     {
>         throw 3.14159 ;
>     }
>
> is a perfectly conforming implementation.  Not a very useful one, of
> course, but the standard doesn't require usefulness.
>
> If you think that this is a misinterpretation of the standard, please
> explain why.

You understand correctly.

> If you think that it is a defect, or at least, something we should
> change, I'm behind you 100%.  It means that in theory, at least, it is
> impossible to write exception safe code without depending on
> implementation defined behavior.

That's already possible.

> (Note, for example, that std::string::swap doesn't have an exception
> specification either.)

Bingo.  That should be changed, just to keep people from making
mistakes with it.  But it's not, strictly speaking, a defect.

>> For basic_string<>::at, we have:
>
>>   21.3.4(3):
>>   Throws: out_of_range if pos >= size().
>
>> That is, at may not throw an exception of any type besides
>> out_of_range, and it may throw no exceptions if pos < size().
>
> All that says is that basic_string<>::at MUST throw the designated
> exception for this particular error.

I'm not even sure it's that strong.

> The paragraph you quote says that a function "can" report an error
> by means of the specified exception.  It does not say that it "shall
> not" raise any other exceptions.
>
> (On rereading it: I don't like the use of "can" either.  Normally,
> requirements on an implementation use the verb "shall".  I would much
> prefer text which clearly required an implementation to report errors
> decribed in the Throws: clause by means of the described exception, or
> one derived from it.  I rather think that this was the intent, but my
> interpretation of "can", in the context of the standard, is that an
> implementation is allowed to, but not required to.)

Correct.  I think it's meant to be "guidance for implementors".

--
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com

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