[boost] Re: Review request: enable_if

From: David Abrahams (dave_at_[hidden])
Date: 2003-07-09 16:16:29

Jaakko Jarvi <jajarvi_at_[hidden]> writes:

> In our last exciting episode Thomas Witt wrote:
>> User-Agent: KMail/1.5
>
>> On Wednesday 09 July 2003 21:09, Jaakko Jarvi wrote:
>> > Where we've used enable_if, it has been very common that the condition
>> > is not just a single traits lookup, but rather a logical expression,
>> > e.g.:
>> >
>> > template <class T, class U>
>> > typename enable_if<is_matrix<T>::value && is_vector<U>::value,...>::type
>> > operator*(const T& t, const U& u);
>
>> Ok I can see the problem, but what about
>
>> template <class T, class U>
>> typename enable_if< mpl::and<is_matrix<T>, is_vector<U> >,...>::type
>> operator*(const T& t, const U& u);
>
> Would work. Requires some knowledge of mpl and a tiny file to be
> included, though. Our view is still that at least the enable_if<bool, T> version 
> is needed. 

Then please spell it enable_if_c, or we'll have boost::mpl::enable_if
with a type first argument :(

> The mpl-aware enable_if would be good to have too.

Yes.

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