Hello,

I've been wondering what the easiest way is to set
the dimension of an array during runtime.

You can't write

   byte[][] a = new byte[size][size];

because the compiler will give an error. The only
thing I've been able to think of is

   byte[][] a;
   a.length = size;
   for (int i; i < size; i++) {
        a[i].length = size;
   }

But it's slower (and less convenient) than
writing

   byte[][] a = new byte[9][9];

> The only thing I've been able to think of is
>
>    byte[][] a;
>    a.length = size;
>    for (int i; i < size; i++) {
>         a[i].length = size;
>    }
Well, you can do at least:

auto a = new byte[][size];
foreach (ref row; a)
  row = new byte[size];

Matthias

On 5-12-2010 19:20, Matthias Walter wrote:
>
>> The only thing I've been able to think of is
>>
>>     byte[][] a;
>>     a.length = size;
>>     for (int i; i<  size; i++) {
>>          a[i].length = size;
>>     }
> Well, you can do at least:
>
> auto a = new byte[][size];
> foreach (ref row; a)
>    row = new byte[size];

That works.

So I can write

   byte[] a = new byte[size];

and

   byte[][] a = new byte[][size];

but not

   byte[][] a = new byte[size][];

or

   byte[][] a = new byte[size][size];

let alone

   byte[size][size] a;


BTW, somebody on stackoverflow just posted an alternative
that comes closest to what I was looking for.

   byte[][] a = new byte[][](size, size);

I saw this notation before but I can't remember where.

Hey, I love D but it can be pretty confusing sometimes :)

Thanks

On 2010-12-05 19:41:50 +0200, user@domain.invalid said:

> Hello,
> 
> I've been wondering what the easiest way is to set
> the dimension of an array during runtime.
> 
> You can't write
> 
>     byte[][] a = new byte[size][size];
> 
> because the compiler will give an error. The only
> thing I've been able to think of is
> 
>     byte[][] a;
>     a.length = size;
>     for (int i; i < size; i++) {
>          a[i].length = size;
>     }
> 
> But it's slower (and less convenient) than
> writing
> 
>     byte[][] a = new byte[9][9];

The syntax might seem a bit misleading, but you can create multidimentional arrays like this:
    int[][] foo = new int[][](5,10);
    foo[4][9] = 31337;

this also works for single-dimention arrays (e.g int[] foo = new int[](size);)

On Sunday 05 December 2010 09:41:50 user@domain.invalid wrote:
> Hello,
> 
> I've been wondering what the easiest way is to set
> the dimension of an array during runtime.
> 
> You can't write
> 
>     byte[][] a = new byte[size][size];
> 
> because the compiler will give an error. The only
> thing I've been able to think of is
> 
>     byte[][] a;
>     a.length = size;
>     for (int i; i < size; i++) {
>          a[i].length = size;
>     }
> 
> But it's slower (and less convenient) than
> writing
> 
>     byte[][] a = new byte[9][9];

auto a = new byte[][](9, 9);

is the way to do it. Otherwise, I believe that you're trying to create a dynamic array of static arrays or somesuch. I'm not sure exactly what the problem is. However, if you just always put the array size in the parens rather than in the brackets when creating an array, then it works correctly. Setting the length in a loop like that (or creating inner arrays with new) is best when you want the inner arrays to be of different length. But when you want them to be the same length, then putting the sizes in the parens in the correct way to go.

- Jonathan M Davis