Re: how can I get a reference of array?

[Ali Çehreli via Digitalmars-d-learn]

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