Hi there,

I know it is possible to declare an associative array which takes arrays as values, i.e.
int[][int] arr;
A sample of this could be
arr[2] = [2, 3, 2, 4, 5];

I was wondering if there was a way to have this with sets instead of arrays. In D, sets are equivalent to red-black trees, afaik. Almost as expected, the declaration
redBlackTree[int] arr;
such that (according to the initial example) arr[2] would be [2, 3, 4, 5]
does not work.

Would anybody know of a workaround?

Hello,

In your case, the type "set of integers" would be written as RedBlackTree!int in D. Note that it starts with an uppercase R, and takes the type of values to contain as template argument (the int after the exclamation mark).

Btw, in the standard library, types always start with an uppercase character, it is a convention that will help you later.

I can then use this type to declare an associated array of sets of integers such as

void main()
{
    RedBlackTree!int[int] assoset;
    assoset[2] = redBlackTree(2, 3, 4, 5);
}

In my example the first line declares an empty associative array that maps sets of integers to integers. I believe this is what you wanted.

The second line may look a bit confusing : redBlackTree starts with a lowercase character and does not contain template type argument. It is a function, not a type. This function takes variadic arguments and creates a RedBlackTree of the type of its arguments. Here, 2, 3, 4, 5 are ints, so it returns a RedBlackTree!int. You may think of it like a constructor or a factory function.

The standard library is full of these convenience functions, because function templates, contrary to struct/class templates, can deduce their template arguments, and avoid the need of precising every detail when it is obsvious.

I hope it helps.

On Tuesday, 12 November 2024 at 00:42:41 UTC, Ralph wrote:

D's std container situation is quite bad. redBlackTree is one workaround about sets for sure.
Another way to simulate it - is using another AA with bool/void parameters.

bool[int][int] dict_of_sets;
dict_of_sets[1] = [1:true, 2:true, 3:true];
dict_of_sets[1][4] = true;
writeln(dict_of_sets); // [1:[4:true, 3:true, 2:true, 1:true]]

On Tuesday, 12 November 2024 at 07:47:58 UTC, Sergey wrote:

Thank you both for your help!