C++ define a type alias 'pointer to array' with keyword using (not typedef)

Question

It is easy to achieve this with typedef:

typedef int (*ptr_arr)[]; // pointer to array

But how to alias the same type as ptr_arr by using C++ using keyword?

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Also would be nice to see (good formatted) syntax difference between aliasing: pointer to array vs array of pointers with both typedef and using.

Answer 1

using         ptr_arr_using = int(*)[];  // pointer to array <-- answer
typedef int (*ptr_arr_typedef)[];        // pointer to array
typedef int  *arr_ptr_typedef [];        // array   of pointers
using         arr_ptr_using = int * [];  // array   of pointers

#include <type_traits>
static_assert(std::is_same_v<ptr_arr_using, ptr_arr_typedef>); // pointer to array
static_assert(std::is_same_v<arr_ptr_using, arr_ptr_typedef>); // array of pointers

static_assert(!std::is_same_v<arr_ptr_using, ptr_arr_using>); // arr_ptr != ptr_arr

Important: () parentheses control operator precedence in declaration

What hinted me to this

An example "alias template" from https://en.cppreference.com/w/cpp/language/type_alias

template<class T> using ptr = T*;
using ptr_arr_using_template = ptr<int[]>; // then IDE showed hint: int(*)[]

Why it is so?

The dispatch order of operators in declaration is the same as in C++ Operator Precedence and Associativity table: https://en.cppreference.com/w/cpp/language/operator_precedence

TL;DR

• [] - precede first and associated Left to right ->
• & * * const/volatile - precede after and associated Right to left <-
• () determine the highest precedence (for operators inside)