• Dennis (33/33) Aug 19 2018 I have a two dimensional static array in a game board struct and
• kinke (16/47) Aug 19 2018 I think the spec is pretty clear; the elements of the
• Dennis (14/18) Aug 19 2018 I can't find where in the spec it says that the elements of the

Dennis <dkorpel gmail.com> writes:

I have a two dimensional static array in a game board struct and 
want to explicitly set the default value for each cell. Now 
typing the whole 9x9 array out would be cumbersome and I can't 
change the default constructor of a struct, so I played around 
with initializers and found some... strange behavior.

Demo:
```
import std.stdio: writeln;

struct T {
     int[3][3] arr = [2, 1];
     this(int stub) {
         arr[0][0] = 9;
     }
}

void main() {
     T.init.writeln;
     T(0).writeln;
}
```
Output:
```
T([[2, 1, 0], [0, 0, 118033674], [723976, 0, 4100]])
T([[9, 2, 2], [1, 1, 1], [0, 0, 0]])
```
So it seems that in the .init value, it puts [2, 1] in the first 
array and the rest is garbage. But in the constructor case, it 
filled the first two static arrays with 2 and 1 and the other one 
is 0 / garbage (can't tell). I turned to the spec:

https://dlang.org/spec/arrays.html#static-init-static

But that doesn't really help specify this case. Should I submit a 
bugzilla issue? I don't know what's supposed to happen here.

And in the mean time, what's the easiest way to initialize a (2d) 
static array with a value?

kinke <noone nowhere.com> writes:

On Sunday, 19 August 2018 at 11:20:41 UTC, Dennis wrote:
 I have a two dimensional static array in a game board struct 
 and want to explicitly set the default value for each cell. Now 
 typing the whole 9x9 array out would be cumbersome and I can't 
 change the default constructor of a struct, so I played around 
 with initializers and found some... strange behavior.

 Demo:
 ```
 import std.stdio: writeln;

 struct T {
     int[3][3] arr = [2, 1];
     this(int stub) {
         arr[0][0] = 9;
     }
 }

 void main() {
     T.init.writeln;
     T(0).writeln;
 }
 ```
 Output:
 ```
 T([[2, 1, 0], [0, 0, 118033674], [723976, 0, 4100]])
 T([[9, 2, 2], [1, 1, 1], [0, 0, 0]])
 ```
 So it seems that in the .init value, it puts [2, 1] in the 
 first array and the rest is garbage. But in the constructor 
 case, it filled the first two static arrays with 2 and 1 and 
 the other one is 0 / garbage (can't tell). I turned to the spec:

 https://dlang.org/spec/arrays.html#static-init-static

 But that doesn't really help specify this case. Should I submit 
 a bugzilla issue? I don't know what's supposed to happen here.

I think the spec is pretty clear; the elements of the 
right-hand-side initializer array are interpreted as per-element 
initializer, i.e., `result[0] = 2, result[1] = 1` (rest: 
default-init). So (latest) LDC outputs

```
T([[2, 2, 2], [1, 1, 1], [0, 0, 0]])
T([[9, 2, 2], [1, 1, 1], [0, 0, 0]])
```

DMD's T.init featuring garbage is clearly a bug, as is the 
divergence wrt. T.init and the initialization of the struct 
literal `T(0)` (which seems to be correct, initializing like LDC, 
but only starting with v2.072). With a non-literal, `auto t = 
T(0); t.writeln();`, the result is `[[9, 1, 0], <garbage from 
T.init>]` again.

So please do file a bugzilla issue.

Dennis <dkorpel gmail.com> writes:

On Sunday, 19 August 2018 at 12:10:08 UTC, kinke wrote:
 I think the spec is pretty clear; the elements of the 
 right-hand-side initializer array are interpreted as 
 per-element initializer, i.e., `result[0] = 2, result[1] = 1` 
 (rest: default-init).

I can't find where in the spec it says that the elements of the 
right-hand-side initializer array are interpreted as per-element 
initializer, or that the rest will be default initialized. But 
that would mean that this works:
```
int[3][3] arr = 0;
```
And it does for a local variable, but for a struct member it says 
(both dmd and ldc):
```
cannot implicitly convert expression 0 of type int to int[3][3]
```
So that should be fixed too.