www.digitalmars.com         C & C++   DMDScript  

digitalmars.D - 2d array

reply chopchop <fakeaddress.chop gmail.com> writes:
I have worked on a little FOSS project (I will ask later for code 
review), I have noticed some limitation on 2d arrays. I haven't 
found the answers on the forum

1) I can not initialize a 2d array in the body of the class,
```
class A
{
   Stuff[][] array2d = Stuff.ONE;
}
```
One must do that in the ctor

2) The following code yields
Error: cannot implicitly convert expression `3` of type `int` to 
`int[20][]`
```
import std;
void main()
{
     writeln("Hello D");
     int[20][20] array2d;
     array2d = 3;
}
```
What I would expect, of course, is to automatically iterate 
through the entire 2d array and set each (i,j) pair to "3".

3) Similarly, it would be nice to have a foreach as follow:
```
foreach ( cell; array2d)// where i = 0 for all j then i = 1 for 
all j, etc

```
I guess I can build smthg with opApply but...
Could even be something like
```
foreach (i, j, cell; array2)
```

THose are just some remarks. Nice to have stuffs, if someone is 
looking that way. Thanks
Dec 31 2021
next sibling parent Era Scarecrow <rtcvb32 yahoo.com> writes:
On Saturday, 1 January 2022 at 00:19:56 UTC, chopchop wrote:

 I have worked on a little FOSS project (I will ask later for 
 code review), I have noticed some limitation on 2d arrays. I 
 haven't found the answers on the forum

 1) I can not initialize a 2d array in the body of the class,
 ```d
 class A
 {
   Stuff[][] array2d = Stuff.ONE;
 }
 ```
 One must do that in the ctor


  If the size is statically known you probably can, however you'd 
be doing it as CTFE.

```d
struct Chess {
   static int[8][8] grid = makeGrid();

   auto makeGrid() {
     int[8][8] tmp;
     //build grid stuff
     return tmp;
   }
}
```

I forget if class variables can be instantiated by default in a 
similar way or not (*like working in Java*).


 2) The following code yields Error: cannot implicitly convert 
 expression `3` of type `int` to `int[20][]`
 ```d
 import std;
 void main()
 {
     writeln("Hello D");
     int[20][20] array2d;
     array2d = 3;
 }
 ```
 What I would expect, of course, is to automatically iterate 
 through the entire 2d array and set each (i,j) pair to "3".


Trying array2d array2d[] array2d[][] all result in the same 
error. I do agree being able to bulk fill or zeroize might be 
nice in some cases. But it's just a little more typing to get the 
same result.

  I wonder if a template mixin would fix this.

```d
foreach(ref y; array2d)
   y[]=3;
```


 3) Similarly, it would be nice to have a foreach as follow:
 ```d
 foreach ( cell; array2d)// where i = 0 for all j then i = 1 for 
 all j, etc
 ```


So like this? Alternatively iota might also do the job.
```d
foreach(i, ref j; array2d)
   j[]=i;
```


 I guess I can build something with opApply but... Could even be 
 something like
 ```d
 foreach (i, j, cell; array2)
 ```


  Hmmm. Default behavior probably is better as is. Consider you 
can alias stuff to build larger stuff. So let's assume i am doing 
some chess stuff.

```d
  alias cell=int;
  alias row=cell[8];
  alias grid=row[8];

  grid board;
```

  Now let's assume i did something like... move piece and 
reference it wrong.

```d
auto movePiece(int x,int y,int x2,int y2) {
   //do checks
   board[x2][y2]=board[x][y];

   //clear piece
   board=0; //should be board[x][y]=0;
}
```

  With default behavior and being more explicit you'd catch a 
simple bug instead of tracing your code for what compiled 
correctly. it's one of the reasons assignment in if statements is 
disallowed as it's easy to mess up. Same for forcibly casting 
rather than assuming down-casting or other is fine.
Dec 31 2021
prev sibling parent reply Dennis <dkorpel gmail.com> writes:
On Saturday, 1 January 2022 at 00:19:56 UTC, chopchop wrote:

 What I would expect, of course, is to automatically iterate 
 through the entire 2d array and set each (i,j) pair to "3".


That's https://issues.dlang.org/show_bug.cgi?id=19178

I've started working on a fix, but haven't finished it yet.
Jan 01 2022
parent chopchop <whateveragain222 gmail.com> writes:
On Saturday, 1 January 2022 at 11:57:41 UTC, Dennis wrote:

 On Saturday, 1 January 2022 at 00:19:56 UTC, chopchop wrote:

 What I would expect, of course, is to automatically iterate 
 through the entire 2d array and set each (i,j) pair to "3".


 That's https://issues.dlang.org/show_bug.cgi?id=19178

 I've started working on a fix, but haven't finished it yet.


Thanks Dennis for your work.
Jan 07 2022