• eastanon (11/11) Jun 02 2018 Does D array implementation support an array of null values?
• Neia Neutuladh (19/30) Jun 02 2018 There are several problems with your code.
• ag0aep6g (2/12) Jun 02 2018 `int[4] a = 5;` is fine, too.
• Timoses (2/13) Jun 05 2018 Does `int[4] nums = void` work?
• Alex (6/7) Jun 05 2018 Work for what?

eastanon <biorelated gmail.com> writes:

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?

Neia Neutuladh <neia ikeran.org> writes:

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`.

ag0aep6g <anonymous example.com> writes:

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.

Timoses <timosesu gmail.com> writes:

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?

Alex <sascha.orlov gmail.com> writes:

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.