Re: Constructing arrays of structs
On Tuesday, 23 January 2024 at 18:15:29 UTC, Stephen Tashiro wrote: If the constructor of a class needs to create an array of structs whose dimensions are inputs, what's the syntax for doing this? For a non-example, the following program errors in main() because in t.array[][] "index [0] is out of bounds". You need to remove `auto` from `auto array = new Point[][](the_dimension,the_dimension);` because it creates a new variable.
Re: Constructing arrays of structs
On Tuesday, 23 January 2024 at 19:32:31 UTC, Stephen Tashiro
wrote:
Thank you.
I don't really understand what the syntax
new Point[][](the_dimension,the_dimension);
denotes. Does it represent a function? To look up this topic,
what are the proper keywords?
By experimentation, I found that "new
Point[the_dimension][the_dimension];" doesn't compile.
This is how you create a _multidimensional array_ in D that's
allocated on the heap.
The wiki mentions this:
https://wiki.dlang.org/Dense_multidimensional_arrays
You could also create a "static array" (on the stack, not heap):
```d
import std.stdio;
void main() {
// allocate on the heap
int[][] matrix = new int[][](5, 2);
writeln(matrix);
// allocate on the stack (I don't actually know why the
dimensions are reversed!
int[2][5] matrix2;
writeln(matrix2);
}
```
This prints `[[0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]` twice as
they're the same matrix.
I normally look at the D website, under the header `Language
Reference`, which links to https://dlang.org/spec/spec.html
If you're looking for just basics, the D Tour is much more
friendly though, click on the `Learn` header:
https://tour.dlang.org/
And then try to find what you want either in `D's Basics` or `D's
Gems` (or the other headers which are specific to other
topics)... these pages normally have links to more in-depth
material, so it's always a good starting point.
I you're looking for standard library help, then instead of
clickin on `Language Reference` on the D's landing page, click on
`Library Reference` instead. Almost all stdlib is either under
`std` or `core`.
Re: Constructing arrays of structs
On Tuesday, January 23, 2024 12:32:31 PM MST Stephen Tashiro via Digitalmars- d-learn wrote: > On Tuesday, 23 January 2024 at 18:23:22 UTC, Renato wrote: > > This works , your mistake was to not actually assign the array > > to the class' field! > > > > Change this line: > > > > ```d > > auto array = new Point[][](the_dimension,the_dimension); > > ``` > > > > To this: > > > > ```d > > this.array = new Point[][](the_dimension,the_dimension); > > ``` > > Thank you. > > I don't really understand what the syntax > > new Point[][](the_dimension,the_dimension); > > denotes. Does it represent a function? To look up this topic, > what are the proper keywords? > > By experimentation, I found that "new > Point[the_dimension][the_dimension];" doesn't compile. Except for the first dimension, all subsequent dimensions have to go in the parens, since putting them between the brackets indicates that that dimension is for a static array rather than a dynamic array, so it would change the type of the array (allowing for dynamic arrays of static arrays). As it is, you can probably only put the first dimension between the brackets, because other languages do that, and allowing it makes it easier to port code. Arguably though, for consistency, you should always put the dimensions between the parens when allocating a new dynamic array. - Jonathan M Davis
Re: Constructing arrays of structs
On Tuesday, 23 January 2024 at 18:23:22 UTC, Renato wrote: This works , your mistake was to not actually assign the array to the class' field! Change this line: ```d auto array = new Point[][](the_dimension,the_dimension); ``` To this: ```d this.array = new Point[][](the_dimension,the_dimension); ``` Thank you. I don't really understand what the syntax new Point[][](the_dimension,the_dimension); denotes. Does it represent a function? To look up this topic, what are the proper keywords? By experimentation, I found that "new Point[the_dimension][the_dimension];" doesn't compile.
Re: Constructing arrays of structs
On Tuesday, 23 January 2024 at 18:15:29 UTC, Stephen Tashiro
wrote:
If the constructor of a class needs to create an array of
structs whose dimensions are inputs, what's the syntax for
doing this?
For a non-example, the following program errors in main()
because in t.array[][] "index [0] is out of bounds".
import std.stdio;
struct Point
{
uint x;
uint y;
void printInfo()
{
printf("(%d $d )",x,y);
}
}
class testClass
{
uint dimension;
Point[][] array;
this(uint the_dimension)
{
dimension = the_dimension;
auto array = new Point[][](the_dimension,the_dimension);
for(uint i = 0; i < dimension; i++)
{
for(uint j = 0; j < dimension; j++)
{
array[i][j].x = i;
array[i][j].y = j;
}
}
}
}
void main()
{
auto t = new testClass(5);
for(uint i = 0; i < t.dimension; i++)
{
for(uint j = 0; j < t.dimension; j++)
{
printf("(%d %d)",t.array[i][j].x, t.array[i][j].y);
//t.array[i][j].printInfo();
}
}
}
This works , your mistake was to not actually assign the array to
the class' field!
Change this line:
```d
auto array = new Point[][](the_dimension,the_dimension);
```
To this:
```d
this.array = new Point[][](the_dimension,the_dimension);
```
Constructing arrays of structs
If the constructor of a class needs to create an array of structs
whose dimensions are inputs, what's the syntax for doing this?
For a non-example, the following program errors in main() because
in t.array[][] "index [0] is out of bounds".
import std.stdio;
struct Point
{
uint x;
uint y;
void printInfo()
{
printf("(%d $d )",x,y);
}
}
class testClass
{
uint dimension;
Point[][] array;
this(uint the_dimension)
{
dimension = the_dimension;
auto array = new Point[][](the_dimension,the_dimension);
for(uint i = 0; i < dimension; i++)
{
for(uint j = 0; j < dimension; j++)
{
array[i][j].x = i;
array[i][j].y = j;
}
}
}
}
void main()
{
auto t = new testClass(5);
for(uint i = 0; i < t.dimension; i++)
{
for(uint j = 0; j < t.dimension; j++)
{
printf("(%d %d)",t.array[i][j].x, t.array[i][j].y);
//t.array[i][j].printInfo();
}
}
}
