Add RequireInputIter on unordered containers

[François Dumont]

On 09/19/2018 11:01 AM, Jonathan Wakely wrote:
> On 19/09/18 08:16 +0200, François Dumont wrote:
>> Unordered containers are missing the std::_RequireInputIter. Even if 
>> deduction guides do have them.
>
> Because that's what the standard requires, see [unord.req] p17.
>
> 17 A deduction guide for an unordered associative container shall not 
> participate in overload resolution if any of
> the following are true:
> — It has an InputIterator template parameter and a type that does not 
> qualify as an input iterator is
> deduced for that parameter.
> — It has an Allocator template parameter and a type that does not 
> qualify as an allocator is deduced
> for that parameter.
> — It has a Hash template parameter and an integral type or a type that 
> qualifies as an allocator is deduced
> for that parameter.
> — It has a Pred template parameter and a type that qualifies as an 
> allocator is deduced for that parameter.
>
> There's no such constraint for the constructors.
>
> It looks like we're not following the last two bullets though. We
> don't constrain the Hash and Pred parameters.
>
>
>
Do you mean that we can't add them on unordered containers themselves ?

At least on the insert method ? I faced an invalid call in my code and 
generated error message was really awful.

François