Question

In C++/CLI, you can specify the following for multidimensional arrays.

array<int, 2>^ Foo = gcnew array<int, 2>(10);
Foo[0, 0] = 1;
Foo[1, 0] = 2;
// ...

I’m trying to replicate the above in the closest syntax possible in standard C++ (C++11 is allowed) via a templated class called my_array.

e.g.

template <typename T, int rank = 1>
    class my_array { };

Is it possible via some comma operator overloading tricks to achieve C++/CLI’s syntax under standard C++, along with overriding my_array’s subscript operator?

Ideally, I’d like the my_array used this way (equivalent to the above example):

my_array<int, 2> Foo = // ... (ignore this part - already implemented)
Foo[0, 0] = 1;
Foo[1, 0] = 2;
// ...

In case anyone’s wondering, I’m creating a C++/CLI equivalent for GCC and currently the framework does not support multidimensional arrays. I’m looking to add that functionality in the closest possible way syntax wise to C++/CLI.

Answer 1

No it is not possible in standard C++. Indeed operator[] can only take a single argument.

You may achieve similar syntax using one of these solutions:

• operator() with several arguments like array(i, j)
• Use a proxy class for arguments, e.g. array[makeIndex(i, j)]
• Using comma operator: array[makeIndex(i), makeIndex(j)]
• Or array[IndexBegin, i, j].

See also this and that questions.

— Optimization note —

In you go the comma route, you’ll be building dynamic lists with the comma operator, and the array will be checking the length of these lists. In a naive implementation these checks will be run-time and redundant (when used in a loop).

Better option: use lists of statically known length (with templates) Like IndexBegin is IndexList<0>, IndexList<N> [comma] int is IndexList<N+1>. Then if your array also know its dimension statically, like a 2D array is Array<2> then you can check at compile time that a 2D array only accepts 2 indices.