US-18: [meta.prop.unary]/6 absence of noexcept should be more explicit or declval used instead

[sdutoit]

N3733 US-18 says:

The trait is_constructible<T, Args...> is defined in terms of a helper template, create<>, that is identical to std::declval<> except for the latter's noexcept clause.

It goes on to propose:

If the absence of noexcept is critical to this definition, insert a Note of explanation; otherwise, excise create<> and reformulate in terms of declval<> the definition of is_constructible.

[sdutoit]

This seems like it requires LWG input; I'm not sure whether or not the absence of noexcept is in fact critical.

[sdutoit]

LWG is opening an issue for this.