I would like to create an associative array that maps a string to a multidimensional dynamic array. In other words, I would like a data structure where I can access elements like this:

foo["key"][0][0]

Is this possible? If so I'm having trouble figuring out the correct syntax, the following (for one dimension) doesn't work:

auto foo = new int[5][string];

compilation fails with the following message:
Error: cannot implicitly convert expression (string) of type string to ulong

Thanks for any help!

On Sun, Sep 9, 2012 at 2:18 PM, Samuele Carcagno <sam.carcagno@gmail.com> wrote:
> I would like to create an associative array that maps a string to a multidimensional dynamic array. In other words, I would like a data structure where I can access elements like this:
>
> foo["key"][0][0]

The type you want is int[][][string]. You can use it like this:

alias int[][][string] MyArray;

void main()
{
    MyArray foo;
    foo["abc"] = [[0,1,2], [3,4], []];
    foo["def"] = [[0]];
    assert(foo["abc"][0][1] == 1);
}

On Sunday, 9 September 2012 at 12:17:47 UTC, Samuele Carcagno wrote:
> I would like to create an associative array that maps a string to a multidimensional dynamic array. In other words, I would like a data structure where I can access elements like this:
>
> foo["key"][0][0]
>
> Is this possible? If so I'm having trouble figuring out the correct syntax, the following (for one dimension) doesn't work:
>
> auto foo = new int[5][string];
>
> compilation fails with the following message:
> Error: cannot implicitly convert expression (string) of type string to ulong
>
> Thanks for any help!

Other way round. Unlike C++, everything goes before the identifier:

--------
import std.stdio;
void main()
{
    int[][][string] foo;
    foo["hello"]=[[1],[2]];
    writeln(foo["hello"]);
    writeln(foo["hello"][0][0]);
}
-------
[[1], [2]]
1
-------
foo is an associative array, the key is "string", and the type is "int[][]"

thanks a lot! both solutions work, to initialize the arrays of int I'm doing:

int[][][string] foo;
foo["key"] = new int[][](6,6);
foo["key"][0][0] = 5;

it seems to work.

On Sun, Sep 9, 2012 at 2:48 PM, Samuele Carcagno <sam.carcagno@gmail.com> wrote:
> thanks a lot! both solutions work, to initialize the arrays of int I'm doing:
>
> int[][][string] foo;
> foo["key"] = new int[][](6,6);
> foo["key"][0][0] = 5;
>
> it seems to work.

Great!

Keep in mind all these structures (AA and dynamic arrays) are reference types. If you copy the associative array, you just copy the references and any change in one will affect the other. Also, internally:

alias int[][][string] MyArray;

void main()
{
    MyArray foo;
    foo["abc"] = [[0,1,2], [3,4], []];
    assert(foo["abc"][0][1] == 1);

// internal copy
    foo["def"] = foo["abc"];
    foo["def"][0][1] = 2;
    assert(foo["abc"][0][1] == 2);

// external copy
    auto bar = foo;
    bar["ghi"] = foo["abc"];
    bar["ghi"][0][1] = 3;
    assert(foo["abc"][0][1] == 3 &&  foo["def"][0][1] == 3);

}

Philippe Sigaud:

> Keep in mind all these structures (AA and dynamic arrays) are
> reference types.

There are bug-prone things you have to keep in mind.

Not exactly a reference type, this is by D specs:


import std.stdio;
import std.array: popFront;
void main() {
     auto d = [1:[2, 3]];
     auto l = d[1];
     auto l2 = l[0];
     l.popFront();
     writeln(d, "  ", l, "  ", l2);
}


Even AAs (I don't know if this is an implementation bug or if this is by D specs, opinions welcome):

void test(int[int] arraya, int x) {
     arraya[x] = x;
}
void main() {
     int[int] d;
     test(d, 0);
     int[int] d0;
     assert(d == d0); // d is empty, 0:0 is lost
     d[1] = 1;
     test(d, 2);
     assert(d == [1: 1, 2: 2]); // now 2:2 is not lost
}

Bye,
bearophile