Does D array implementation support an array of null values?

int a[4] = null;

But I ran into a type error while checking if a[i] is null

foreach(i; 0..3){
 if(i == null){
   writeln("it is null");
   }
  }
}

How do you set fixed size array of null values and check if they are null?

On Saturday, 2 June 2018 at 18:10:38 UTC, eastanon wrote:
> Does D array implementation support an array of null values?
>
> int a[4] = null;
>
> But I ran into a type error while checking if a[i] is null
>
> foreach(i; 0..3){
>  if(i == null){
>    writeln("it is null");
>    }
>   }
> }
>
> How do you set fixed size array of null values and check if they are null?

There are several problems with your code.

1. `int a[4]` should be `int[4] a`. You probably see a warning about using the C-style array syntax.

2. `int[4] a = null` treats the initialization as a copy from an array whose value is null. If you run just that line of code, it will produce an error at runtime: "object.Error@(0): Array lengths don't match for copy: 0 != 4"

If you want to initialize every member of an array with a value, you write it as:

    int[4] a;
    a[] = 5;

3. `foreach (i; 0..3)` will iterate through a range of integers: 0, 1, and 2. You haven't touched your array.

4. `i == null` is trying to compare an integer, which can never be null, to null. You either want to use std.typecons.Nullable (if you just want integers-that-might-be-null) or an array of pointers to integers (if you want reference semantics).

5. Usually, you want to use `i is null` instead of `i == null`.

On 06/02/2018 08:35 PM, Neia Neutuladh wrote:
> 2. `int[4] a = null` treats the initialization as a copy from an array whose value is null. If you run just that line of code, it will produce an error at runtime: "object.Error@(0): Array lengths don't match for copy: 0 != 4"
> 
> If you want to initialize every member of an array with a value, you write it as:
> 
>      int[4] a;
>      a[] = 5;

`int[4] a = 5;` is fine, too.

On Saturday, 2 June 2018 at 18:10:38 UTC, eastanon wrote:
> Does D array implementation support an array of null values?
>
> int a[4] = null;
>
> But I ran into a type error while checking if a[i] is null
>
> foreach(i; 0..3){
>  if(i == null){
>    writeln("it is null");
>    }
>   }
> }
>
> How do you set fixed size array of null values and check if they are null?

Does `int[4] nums = void` work?

On Tuesday, 5 June 2018 at 14:52:28 UTC, Timoses wrote:
> Does `int[4] nums = void` work?

Work for what?

If you avoid initialization, then the variable(s) are not initialized.

https://dlang.org/spec/declaration.html#void_init


However, an int is not nullable and always contains a value.