Here is a simple code snippet:
class A {
	public int[] arr;
}

class B {
	public int[] arr;
}

void main()
{
	int[] arr;

	A a = new A;
	B b = new B;
	a.arr = arr;
	b.arr = arr;


	arr ~= 1;
	arr ~= -2;

	foreach(data; a.arr)
	{
		writeln(data);
	}

	foreach(data; b.arr)
	{
		writeln(data);
	}
}

it prints nothing, I know that a.arr and b.arr are all slices of arr.

But if a and b want to reference the global arr, it means that any changes in arr will be seen by a and b, and vice versa.

How to?

Thanks ahead.

void test(ref int[] arr) {
	arr ~= 4;
}

It is something like ref variables. But ref just be used in
function declaration.

On 02/04/2015 10:42 PM, zhmt wrote:
> Here is a simple code snippet:
> class A {
>      public int[] arr;
> }
>
> class B {
>      public int[] arr;
> }
>
> void main()
> {
>      int[] arr;
>
>      A a = new A;
>      B b = new B;
>      a.arr = arr;
>      b.arr = arr;
>
>
>      arr ~= 1;
>      arr ~= -2;
>
>      foreach(data; a.arr)
>      {
>          writeln(data);
>      }
>
>      foreach(data; b.arr)
>      {
>          writeln(data);
>      }
> }
>
> it prints nothing, I know that a.arr and b.arr are all slices of arr.
>
> But if a and b want to reference the global arr, it means that any
> changes in arr will be seen by a and b, and vice versa.
>
> How to?
>
> Thanks ahead.

First, in order to get what you want, add 4 starts and 2 ampersands so that there is one array and two pointers to it:

import std.stdio;

class A {
    public int[] * arr;    // <-- *
}

class B {
    public int[] * arr;    // <-- *
}

void main()
{
    int[] arr;

    A a = new A;
    B b = new B;
    a.arr = &arr;          // <-- &
    b.arr = &arr;          // <-- &


    arr ~= 1;
    arr ~= -2;

    foreach(data; *a.arr)  // <-- *
    {
        writeln(data);
    }

    foreach(data; *b.arr)  // <-- *
    {
        writeln(data);
    }
}

The output:

1
-2
1
-2

Appending to a slice breaks its sharing relationship with other slices. The following article is very informative:

  http://dlang.org/d-array-article.html

Ali

@Ali

I know the direction now, I should learn more about the pointers. Thx very much.

Will arr.ptr change in the future?

As the array add more members , it need more memroy, then remalloc may be called, the pointer maybe change, then the stored pointer will be invalid.

Will this happen?

The behavior of array is more or less unpredictable.

If it is always a reference like class , it will be more predictable.

zhmt:

> Will arr.ptr change in the future?
>
> As the array add more members , it need more memroy, then remalloc may be called, the pointer maybe change, then the stored pointer will be invalid.
>
> Will this happen?

Yes, it can happen.

Bye,
bearophile

Sorry, I misunderstand the meaning of array pointer, it is not equals to arr.ptr.

The array pointer meets my need perfectly .

Ignore my replies above, Sorry!!!

On Thursday, 5 February 2015 at 08:58:47 UTC, bearophile wrote:
> zhmt:
>
>> Will arr.ptr change in the future?
>>
>> As the array add more members , it need more memroy, then remalloc may be called, the pointer maybe change, then the stored pointer will be invalid.
>>
>> Will this happen?
>
> Yes, it can happen.
>
> Bye,
> bearophile

Thx. I understand the difference between array pointer and arr.ptr, they are not the same thing.

"Ali Çehreli" <acehreli@yahoo.com> schrieb im Newsbeitrag news:mav4a1$l3a$1@digitalmars.com...
> On 02/04/2015 10:42 PM, zhmt wrote:
> The following article is very informative:
>
>   http://dlang.org/d-array-article.html

Nice and important article.

But: How could I have looked this up this myself?
What should be the official path to this link?

I tried "Books&Articles" and "Community => More Links"
and could not find it.