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
