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digitalmars.D.learn - difficulty with rectangular arrays

reply Moth <postmaster gmail.com> writes:
hullo all. i've encountered a bizzare inconsistency.

the following is the [D spec on rectangular 
arrays](https://dlang.org/spec/arrays.html#rectangular-arrays):

```
void main()
{
     import std.stdio: write, writeln, writef, writefln;
     double[6][3] matrix = 0; // Sets all elements to 0.
     writeln(matrix); // [[0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0], 
[0, 0, 0, 0, 0, 0]]
}
```


however, when i attempt to place the very same code within a 
class...

```
class ExampleClass
{
     double[6][3] matrix = 0; //fails to compile - "Error: cannot 
implicitly convert expression `0` of type `int` to `double[6][3]`"
}
```

evidently i'm doing something wrong here, but i can't understand 
what or why. what's going on? have i misread the spec?
Jun 11 2021
next sibling parent reply jfondren <julian.fondren gmail.com> writes:
On Friday, 11 June 2021 at 08:30:29 UTC, Moth wrote:

 ```
 class ExampleClass
 {
     double[6][3] matrix = 0; //fails to compile - "Error: 
 cannot implicitly convert expression `0` of type `int` to 
 `double[6][3]`"
 }
 ```

 evidently i'm doing something wrong here, but i can't 
 understand what or why. what's going on? have i misread the 
 spec?


The example in the spec is in a function body and you've copied
it to a class body, where the writeln() would also be in error.
I find https://dlang.org/spec/grammar.html quite hard to read
but I imagine there's a state/declaration distinction there, 
despite
the code looking the same.

This works:

```d
class Example {
     double[6][3] matrix;
     this() {
         matrix = 0;
     }
}
```
Jun 11 2021
parent Moth <postmaster gmail.com> writes:
On Friday, 11 June 2021 at 08:40:51 UTC, jfondren wrote:


 The example in the spec is in a function body and you've copied
 it to a class body, where the writeln() would also be in error.
 I find https://dlang.org/spec/grammar.html quite hard to read
 but I imagine there's a state/declaration distinction there, 
 despite
 the code looking the same.

 This works:

 ```d
 class Example {
     double[6][3] matrix;
     this() {
         matrix = 0;
     }
 }
 ```


i see.
that's a bummer - i knew the `writeln()` wouldn't work in a class 
body, but i assumed that because other initializations work [e.g, 
`int myint = 4;` or `int[69] funny = 420;`], this case would be 
much the same. ah well.

off topic, your baba is you avatar is very cute.
Jun 11 2021
prev sibling parent Dennis <dkorpel gmail.com> writes:
On Friday, 11 June 2021 at 08:30:29 UTC, Moth wrote:

 what's going on?


It's a bug:
[Issue 19178 - Static initialization of 2d static arrays in 
structs produces garbage or doesn't compile 
sometimes](https://issues.dlang.org/show_bug.cgi?id=19178)
Jun 11 2021