Re: Struct array assignment behaviour using example from Programming in D, chapter 78
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!
Re: Struct array assignment behaviour using example from Programming in D, chapter 78
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
Re: Struct array assignment behaviour using example from Programming in D, chapter 78
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.
Re: Struct array assignment behaviour using example from Programming in D, chapter 78
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
Re: Struct array assignment behaviour using example from Programming in D, chapter 78
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!
Struct array assignment behaviour using example from Programming in D, chapter 78
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?
