[boost] Re: Safe bool idiom

From: David Abrahams (dave_at_[hidden])
Date: 2003-09-11 10:52:44

Douglas Gregor <gregod_at_[hidden]> writes:

> On Thursday 11 September 2003 09:36 am, Daniel Frey wrote:
>> This new idiom should be as safe as the current one, but it uses a real
>> operator bool() for bool conversion, so no overhead can slip in. To be
>> fair, it also has one drawback: The error message a user receives when
>> converting a shared_ptr to int, float, ... is not as nice as today.
>
> My only remaining concern with the new idiom is that it breaks is_convertible. 
> With the member function pointer version, 
> is_convertible<something_bool_testable, int>::value == false; with the 
> private conversion to an integral type, this results in a compiler error. 
>
> I don't know what to do about this, or if it will break much user code, but it 
> will break some code.

Breaking is_convertible is bad.  

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com