How to use a cv-qualifier for a method that returns a reference to an array?

Question

If I have a member function which returns a reference to an array (https://stackoverflow.com/a/5399014/4304120), how can I add a const qualifier to the function? This code doesn't compile under Visual C++ 2010.

struct A
{
    int data[10];

    // this compiles
    const int (&f1())[10]
    {
        return data;
    }

    // error C2143: syntax error : missing ';' before '<cv-qualifer>'
    const int (&f2())[10] const
    {
        return data;
    }
};

Answer 1

I'll propose few solutions which are in my opinion more readable than the extremely direct answer to this question. I'm sure there are C grammar enthusiasts out there and I apologize to them for I have terrible memory and I'm not able to remember those C rules.

Type alias

You can avoid the weird C-based grammar by using a type alias:

struct A {
    using data_type = int[10];
    data_type data;
    data_type& f1() { return data; }
    data_type const& f2() const { return data; }
};

Live demo

or with typedef (for before C++11):

struct A {
    typedef int data_type[10];
    data_type data;
    data_type& f1() { return data; }
    data_type const& f2() const { return data; }
};

Live demo

Auto

Since C++14 you can also use auto return types:

struct A {
    int data[10];
    auto& f1() { return data; }
    auto const& f2() const { return data; }
};

Live demo

Standard array

As of C++11 you can also just use std::array:

struct A {
    using data_type = std::array<int, 10>;
    data_type data;
    data_type& f1() { return data; }
    data_type const& f2() const { return data; }
};

Live demo

and simplify it to:

struct A {
    std::array<int, 10> data;
};

Live demo

which is somewhat functionally equivalent but easier on the eyes.