I have been playing with the matrix example given at the end of chapter 78 of Ali Çehreli's fabulous book and am having problems with overloading the opAssign operator.

rows is a private int[][] in a Matrix struct.

I have added the following ...

Matrix opAssign(int[][] arr)
{
    this.rows = arr;
    // rows = arr // does not work either ...
    return this;
}

However this does not work (no error occurs, it just doesn't do anything) but this does work ...

Matrix opAssign(int[][] arr)
{
    foreach(i, row; rows){
        row[] = arr[i];
    }
    return this;
}

The second is not efficient since it has to loop to assign the array. Is there a more efficient way of overwriting the array?

On Thursday, 24 March 2016 at 17:24:38 UTC, data pulverizer wrote:
> I have been playing with the matrix example given at the end of chapter 78 of Ali Çehreli's fabulous book and am having problems with overloading the opAssign operator.
>
> rows is a private int[][] in a Matrix struct.
>
> I have added the following ...
>
> Matrix opAssign(int[][] arr)
> {
>     this.rows = arr;
>     // rows = arr // does not work either ...
>     return this;
> }
>
> However this does not work (no error occurs, it just doesn't do anything) but this does work ...
>
> Matrix opAssign(int[][] arr)
> {
>     foreach(i, row; rows){
>         row[] = arr[i];
>     }
>     return this;
> }
>
> The second is not efficient since it has to loop to assign the array. Is there a more efficient way of overwriting the array?

Sorry. Please disregard. I'll drive home and ask this question properly!

On 03/24/2016 10:24 AM, data pulverizer wrote:
> I have been playing with the matrix example given at the end of chapter
> 78 of Ali Çehreli's

For reference, it's "Multi-dimensional operator overloading example" here:

  http://ddili.org/ders/d.en/templates_more.html

>having problems with overloading the opAssign operator.
>
> rows is a private int[][] in a Matrix struct.
>
> I have added the following ...
>
> Matrix opAssign(int[][] arr)
> {
>      this.rows = arr;
>      // rows = arr // does not work either ...
>      return this;
> }
>
> However this does not work (no error occurs, it just doesn't do
> anything)

How are you testing it? The following worked for me:

1) Added that opAssign() to the struct. (Verified that it gets called.)

2) Tested with the following code:

    auto m2 = Matrix();
    auto rows = [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ];
    m2 = rows;

    writeln(m2);

(I've tested with a dynamically generated 'rows' as well.)

Ali

On Thursday, 24 March 2016 at 18:46:14 UTC, Ali Çehreli wrote:
> On 03/24/2016 10:24 AM, data pulverizer wrote:
> > I have been playing with the matrix example given at the end
> of chapter
> > 78 of Ali Çehreli's
>
> For reference, it's "Multi-dimensional operator overloading example" here:
>
>   http://ddili.org/ders/d.en/templates_more.html
>
> >having problems with overloading the opAssign operator.
> >
> > rows is a private int[][] in a Matrix struct.
> >
> > I have added the following ...
> >
> > Matrix opAssign(int[][] arr)
> > {
> >      this.rows = arr;
> >      // rows = arr // does not work either ...
> >      return this;
> > }
> >
> > However this does not work (no error occurs, it just doesn't
> do
> > anything)
>
> How are you testing it? The following worked for me:
>
> 1) Added that opAssign() to the struct. (Verified that it gets called.)
>
> 2) Tested with the following code:
>
>     auto m2 = Matrix();
>     auto rows = [ [ 1, 2 ], [ 3, 4 ], [ 5, 6 ] ];
>     m2 = rows;
>
>     writeln(m2);
>
> (I've tested with a dynamically generated 'rows' as well.)
>
> Ali

Thank you. Let me try to ask the question again. The problem I am experiencing is to do with opIndexAssign().

I added the following public operators:

	Matrix opAssign(int[][] arr)
	{
		writeln(__FUNCTION__);
		this.rows = arr;
		return this;
	}

	Matrix opAssign(Matrix mat)
	{
		writeln(__FUNCTION__);
		this.rows = mat.rows;
		return this;
	}

	Matrix opIndexAssign(A...)(int[][] arr, A arguments)
		if(A.length <= 2){
		writeln(__FUNCTION__);
		Matrix subMatrix = opIndex(arguments);
		assert(((arr.length == subMatrix.nrow()) & (arr[0].length == subMatrix.ncol())),
			"Array dimension do not match matrix replacement.\n");
		/*foreach(i, row; subMatrix.rows){
			row[] = arr[i];
		}*/
		subMatrix = arr; // Does not work
		return subMatrix;
	}

	Matrix opIndexAssign(A...)(Matrix mat, A arguments)
	if(A.length <= 2){
		writeln(__FUNCTION__);
		Matrix subMatrix = opIndex(arguments);
		assert(((mat.nrow() == subMatrix.nrow()) & (mat.ncol() == subMatrix.ncol())),
		"Array dimension do not match matrix replacement.\n");
		/*foreach(i, row; subMatrix.rows){
			row[] = mat.rows[i];
		}*/
		subMatrix = mat; // Does not work
		return subMatrix;
	}




void main(){
	// Here we test opAssign [][]int
	auto a = Matrix();
	a = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]; // this works
	writeln(a);
	// opIndexAssign int[][]
	a[0..2, 0..2] = [[88, 88], [88, 88]]; // this does not work
	writeln(a);
	auto b = Matrix();
	// opAssign Matrix
	b = a; // this works
	writeln(b);
	b = [[88, 88, 88, 88], [88, 88, 88, 88], [88, 88, 88, 88], [88, 88, 88, 88]];
	// opIndexAssign Matrix
	b[0..3, 0..3] = a; // this does not work
	writeln(b);
}


If you uncomment the foreach lines, the opIndexAssign() work.

On 03/25/2016 12:00 AM, data pulverizer wrote:
> On Thursday, 24 March 2016 at 18:46:14 UTC, Ali Çehreli wrote:
>> On 03/24/2016 10:24 AM, data pulverizer wrote:
>> > I have been playing with the matrix example given at the end
>> of chapter
>> > 78 of Ali Çehreli's
>>
>> For reference, it's "Multi-dimensional operator overloading example"
>> here:
>>
>>   http://ddili.org/ders/d.en/templates_more.html
>>
>> >having problems with overloading the opAssign operator.

> Thank you. Let me try to ask the question again. The problem I am
> experiencing is to do with opIndexAssign().
>
> I added the following public operators:
>
>      Matrix opAssign(int[][] arr)
>      {
>          writeln(__FUNCTION__);
>          this.rows = arr;
>          return this;
>      }

The problem is due to the aliasing of 'rows' members of Matrix objects. subMatrix is supposed to be a reference into some elements of an existing Matrix. As soon as we do the above assignment, this Matrix (which may be a subMatrix in a specific context) breaks lose from its actual Matrix elements.

We need to implement the function above "in place":

    Matrix opAssign(int[][] arr)
    {
        writeln(__FUNCTION__);

        if (rows.length < arr.length) {
            rows.length = arr.length;
        }

        foreach (i, row; arr) {
            const newLength = row.length;

            if (rows[i].length < newLength) {
                rows[i].length = newLength;
            }
            rows[i][0..newLength] = row[];
        }

        return this;
    }

(There must be an existing function that does that.)

>      Matrix opAssign(Matrix mat)
>      {
>          writeln(__FUNCTION__);
>          this.rows = mat.rows;

Same thing applies above: We need to assign to this.rows in place (which is easier by taking advantage of the previous function):

        this = mat.rows;

>          return this;
>      }

No changes needed for the other two functions but I would 'return this' instead of 'return subMatrix' for them as well.

Ali

On Friday, 25 March 2016 at 08:53:20 UTC, Ali Çehreli wrote:
> On 03/25/2016 12:00 AM, data pulverizer wrote:
> > On Thursday, 24 March 2016 at 18:46:14 UTC, Ali Çehreli wrote:
> >> On 03/24/2016 10:24 AM, data pulverizer wrote:
> >> > I have been playing with the matrix example given at the
> end
> >> of chapter
> >> > 78 of Ali Çehreli's
> >>
> >> For reference, it's "Multi-dimensional operator overloading
> example"
> >> here:
> >>
> >>   http://ddili.org/ders/d.en/templates_more.html
> >>
> >> >having problems with overloading the opAssign operator.
>
> > Thank you. Let me try to ask the question again. The problem
> I am
> > experiencing is to do with opIndexAssign().
> >
> > I added the following public operators:
> >
> >      Matrix opAssign(int[][] arr)
> >      {
> >          writeln(__FUNCTION__);
> >          this.rows = arr;
> >          return this;
> >      }
>
> The problem is due to the aliasing of 'rows' members of Matrix objects. subMatrix is supposed to be a reference into some elements of an existing Matrix. As soon as we do the above assignment, this Matrix (which may be a subMatrix in a specific context) breaks lose from its actual Matrix elements.
>
> We need to implement the function above "in place":
>
>     Matrix opAssign(int[][] arr)
>     {
>         writeln(__FUNCTION__);
>
>         if (rows.length < arr.length) {
>             rows.length = arr.length;
>         }
>
>         foreach (i, row; arr) {
>             const newLength = row.length;
>
>             if (rows[i].length < newLength) {
>                 rows[i].length = newLength;
>             }
>             rows[i][0..newLength] = row[];
>         }
>
>         return this;
>     }
>
> (There must be an existing function that does that.)
>
> >      Matrix opAssign(Matrix mat)
> >      {
> >          writeln(__FUNCTION__);
> >          this.rows = mat.rows;
>
> Same thing applies above: We need to assign to this.rows in place (which is easier by taking advantage of the previous function):
>
>         this = mat.rows;
>
> >          return this;
> >      }
>
> No changes needed for the other two functions but I would 'return this' instead of 'return subMatrix' for them as well.
>
> Ali

That's great! Thank you very much for the fix and extra suggestions, and for your patience putting up with my poorly formulated question! Looks like I need to go and read all the structs and operators chapters thoroughly!