Hi,

my name is Mike and I'm new to D (coming from a Javabackground) and for fun I'm trying to learn D now.
I created a simple class

class Block {

    int a, b;
    this() {}

}

And now I have a dynamic array of objects of this class in another class:

class Foo {

     Block[] array  = new Block[](10);

     this() {
       for (int i = 0; i < array.length; i++) {
          array[i] = new Block();
       }
     }
}

How would a proper destructor of class Foo look like?
Is it enough to set "array" to null? Or do I have to set every element of the array to null and then the array, or nothing of that at all because the garbage collecter collects it, if the reference to Foo is set to null?

On Thursday, 13 June 2019 at 16:08:52 UTC, Mike wrote:
> or nothing of that at all because the garbage collecter collects it, if the reference to Foo is set to null?

That. [The init loop can be shortened to `foreach (ref b; array) b = new Block();`.]

On Thursday, 13 June 2019 at 16:08:52 UTC, Mike wrote:
> How would a proper destructor of class Foo look like?
> Is it enough to set "array" to null? Or do I have to set every element of the array to null and then the array, or nothing of that at all because the garbage collecter collects it, if the reference to Foo is set to null?

Nothing at all, GC will take care. As long as your Block class doesn't create any system resources that must be discarded.

On Thursday, 13 June 2019 at 16:08:52 UTC, Mike wrote:
> Hi,
>
> my name is Mike and I'm new to D (coming from a Javabackground) and for fun I'm trying to learn D now.
> I created a simple class
>
> class Block {
>
>     int a, b;
>     this() {}
>
> }
>
> And now I have a dynamic array of objects of this class in another class:
>
> class Foo {
>
>      Block[] array  = new Block[](10);
>
>      this() {
>        for (int i = 0; i < array.length; i++) {
>           array[i] = new Block();
>        }
>      }
> }
>
> How would a proper destructor of class Foo look like?
> Is it enough to set "array" to null? Or do I have to set every element of the array to null and then the array, or nothing of that at all because the garbage collecter collects it, if the reference to Foo is set to null?

Opposed to Java, D's member variables are static initialised. There is one default value for "array" that is shared between all instances of Foo. This allows for compiler optimisations of primitives (baking in a int value of 5 into the class definition, but gives unexpected behaviour for reference types.

https://run.dlang.io/is/UNp5Al

In this example, two instances of Foo are created. The constructor is run both times. However, they act on the same array object. So initialisation of the second Foo will modify references data of the first Foo. As a check, the first object of both Foos are compared by reference.

Java allows you to define a block of code in your class that is run on construction, e.g.
public class JavaClass {
    {
        doStuff();
    }
    int x = initializeX();
}
It makes for fun questions on things like OCA certificates. However, D doesn't allow that. All initialisation code is placed in the constructor, e.g.

this() {
    array = new Block[](10);
    // ...
}

(Of course you can call other methods from there. In fact, constructor rules are slightly relaxed compared to Java.)

On Friday, 14 June 2019 at 07:52:24 UTC, Marco de Wild wrote:
> On Thursday, 13 June 2019 at 16:08:52 UTC, Mike wrote:
> Opposed to Java, D's member variables are static initialised.

Is there any documentation about this? I find it unexpected.

On Friday, 14 June 2019 at 11:10:58 UTC, rumbu wrote:
> On Friday, 14 June 2019 at 07:52:24 UTC, Marco de Wild wrote:
>> On Thursday, 13 June 2019 at 16:08:52 UTC, Mike wrote:
>> Opposed to Java, D's member variables are static initialised.
>
> Is there any documentation about this? I find it unexpected.

https://dlang.org/spec/class.html#static-constructor

«All member initializations must be determinable by the compiler at compile time, hence there is no order-of-evaluation dependency for member initializations, and it is not possible to read a value that has not been initialized. Dynamic initialization is performed by a static constructor»