Default implementation of std::hash template

[Jonathan Wakely]

On 6 March 2013 19:13, Daniel Frey wrote:
>
> we can have both is_hashable and the static_assert, which fires if someone tries to instantiate the template:
>
>   std::unordered_set< std::pair< int, int > > dummy; // fires the static_assert.
>
> What do you think?

On the trunk we just have an undefined primary template, there's no
static_assertion, and your trait works with GCC 4.8 (after adding the
missing closing parenthesis for the sizeof)