[cfe-dev] Exception Specs & Redeclarations

[Sebastian Redl]

On 06.03.2011, at 19:27, Douglas Gregor wrote:

> 
> On Mar 6, 2011, at 4:35 AM, Sebastian Redl wrote:
> 
>> 
>> On 06.03.2011, at 12:54, Sebastian Redl wrote:
>> 
>>> Hi,
>>> 
>>> My opinion is that the standard is broken here. noexcept(false) shouldn't be compatible with throw(X) specifiers. That can only lead to chaos.
>>> 
>>> But if there are important reasons to keep the standard as it is, what would be the best way to implement this?
>> 
>> After looking through the standard history, I now know the rationale behind this compatibility feature. However, the problem I pointed out remains. I am not sure that the benefit (can update header files to avoid deprecation warnings in client code, without having to update source files) outweighs the cost (really messy redecl merging - and I can't believe Clang is the only compiler to suffer from this).
>> 
>> However, assuming that others do not share my opinion here, I think a narrower wording would be beneficial. In particular:
>> 1) A throw(X) specifier *on a definition only* should be compatible with noexcept(false) on declarations. (I realise that would be tricky to get right in Clang.)
>> and/or 2) The compatibility rule does not apply to function templates. (Or at least, and that's what I'm actually going to implement for now, dependent noexcept specifiers are incompatible with dynamic specifiers.)
> 
> Check out 
> 
> 	http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1073
> 
> which strikes the problematic compatibility rule. Let's assume the proposed resolution; IIRC, it's what GCC does.

Happy to oblige.

Sebastian