c++ - Why can't unique_ptr's template arguments be deduced?

Question

When you have class template argument deduction available from C++17, why can't you deduce the template arguments of std::unique_ptr? For example, this gives me an error:

std::unique_ptr smp(new D);

That says "Argument list of class template is missing".

Shouldn't the template arguments (at least the pointer type) be deducable?

See this:

any declaration that specifies initialization of a variable and variable template

Answer 1

Lets look at new int and new int[10]. Both of those return an int*. There is no way to tell if you should have unique_ptr<int> or unique_ptr<int[]>. That right there is enough not to provide any sort of deduction guide.