Hi

Program has two steps:

1. Creates an array (int[] A), whose size and element values are only known at run-time.

Then:
2. The elements (but not the array size) are further processed in a way that may or may not alter their value.

Requirement: to identify the indices (if any) of the elements whose value changed in step 2.

What is the recommended way to do this?

Creating a step 1.5:

int[] B = A;

And then step 2.5:

for (int j=0, j < A.length, j = j+1) {

   if (B[j] != A[J]) {
      < write the j value away somewhere>
   } else {
   }
}

Won't work, as any step 2 changes to A will be reflected in B.

In passing,is 'dynamic array' a good title for a structure/concept that seems more of a 'view'?
Surely 'dynamic array' is best used for something that is (no more than) a static array whose dimensions can vary at run time?

Best regards

On Sunday, 13 November 2022 at 14:28:45 UTC, DLearner wrote:

int[] B = A;

auto B = A.dup;

This will create a copy of A rather than referencing to the same buffer in memory.

On Sunday, 13 November 2022 at 14:39:26 UTC, Siarhei Siamashka wrote:

int[] B = A;

auto B = A.dup;

Tested:

void main() {

   import std.stdio;


   struct test_struct {
      char[] Txt;
   }

   test_struct[] A;


   A.length = 1;
   A[0].Txt.length = 1;
   A[0].Txt[0] = 'X';

   writeln(A);


   auto B = A.dup;

   writeln(A, B);

   A[0].Txt[0] = 'Y';

   writeln(A, B);
}

Got:

[test_struct("X")]
[test_struct("X")][test_struct("X")]
[test_struct("Y")][test_struct("Y")]

Expected last line to be Y,X not Y,Y.

On Sunday, 13 November 2022 at 15:45:40 UTC, DLearner wrote:

   struct test_struct {
      char[] Txt;
   }
   test_struct[] A;
   auto B = A.dup;

But A is not an int[] in your new example. You need a "deep copy" and I can see that similar questions had been asked in this forum before: https://forum.dlang.org/thread/yzvcyyqadpttqvtiefhn@forum.dlang.org

Maybe you can add a copy constructor to your struct, which would dup Txt?

On Sunday, 13 November 2022 at 16:11:17 UTC, matheus. wrote:
[...]

Thank you - your suggestion worked.

The slight generalisation shown at bottom also worked.

However, is there a way of avoiding the for-loop?
Things like

B[].Txt = A[].Txt.dup;

did not work for me.

void main() {

   import std.stdio;

   int index;
   struct test_struct {
      char[] Txt;
   }

   test_struct[] A;

   A.length = 2;
   A[0].Txt.length = 1;
   A[1].Txt.length = 1;

   A[0].Txt[0] = 'W';
   A[1].Txt[0] = 'X';

   writeln(A);

   auto B = A.dup;
   for (index = 0; index < A.length; index = index + 1) {
      B[index].Txt = A[index].Txt.dup;
   }

   writeln(A, B);

   A[0].Txt[0] = 'Y';
   A[1].Txt[0] = 'Z';

   writeln(A, B);
}