[patch] libstdc++/69240 generic operator!= for random number distributions

[Marc Glisse]

On Thu, 14 Jan 2016, Jonathan Wakely wrote:

> On 14/01/16 20:13 +0100, Marc Glisse wrote:
>> I didn't think about it much, but I am worried that __random_not_eq will 
>> accidentally become an associated namespace for more classes than we would 
>> expect.
>
> Yes, it would be an associated namespace for types that derive from
> the distributions, or class template specializations that use the
> distributions as template arguments.
>
> We could constrain the generic operator== and operator!= to only match
> types that we want it to match, e.g. by having a type trait that is
> true for all our distributions and their parameter types. That would
> mean adding a specialization of it for each distribution and parameter
> type:
>
> template<typename _IntType>
>   struct
>   __is_comparable_random_dist<uniform_int_distribution<_IntType>>
>   : true_type { };
>
> Having to do that for every type removes some of the advantages of the
> patch, but would still be less code overall.
>
> If the operators are constrained in that way then I don't think it's a
> problem that the namespaces would be associated with more types,
> because there's nothing else in those namespaces that could be found
> by ADL.

Once you constrain, you could even use 'std' as the associated namespace 
;-)

-- 
Marc Glisse