It is sufficient to have name and type. There is no need for the result
"to know" what exact expression was used to define the column.
Surprisingly, template alias creates new templates (in contrast to
non-template using, which really just creates an alias of a type).
template<typename T> struct A{};
struct X
{
template<typename T>
using U = A<T>;
};
struct Y
{
template<typename T>
using U = A<T>;
template<>
using U<int> = X;
};
template<template<typename> class X>
struct Z{};
static_assert(std::is_same<X::U<int>, Y::U<int>>::value, "class aliases are really just aliases");
static_assert(not std::is_same<Z<X::U>, Z<Y::U>>::value, "template aliases are new templates");
int main()
{
}
Roland Bock