Difference between type alias and using-declaration

问题

Is there any difference between using a type alias and alias template on the one hand and using-declaration on the other hand defined as follows:

Given a class definition in a namespace scope:

namespace ns1
{
template< typename T >
struct A {};
}

And given another namespace, which introduces the A symbol by two different ways. First of them is type alias (alias template):

namespace ns2
{
template< typename T >
using A = ns1::A< T >; // match type-id
}

Second one is using-declaration:

namespace ns2
{
using ns1::A;
}

Is there any difference for ADL and for any other using contexts in ns1 scope (reopened), in ns2 scope or in outer scope?

来源：https://stackoverflow.com/questions/33602658/difference-between-type-alias-and-using-declaration