Struct array assignment behaviour using example from Programming in D, chapter 78

[data pulverizer via Digitalmars-d-learn]

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.