Re: How to obtain Variant underlying type?
On Monday, 11 July 2022 at 06:59:32 UTC, anonymouse wrote:
I did search for a better solution and came across...
https://tastyminerals.github.io/tasty-blog/dlang/2020/03/22/multidimensional_arrays_in_d.html
I like it!
It's been a good collaboration...
```d
import std.variant;
auto generate(T)(size_t x, size_t y) {
T[][] result;
ubyte[] arr = new ubyte[x * y * T.sizeof];
size_t m = y * T.sizeof;
foreach (i; 0 .. x) {
size_t n = i * m;
result ~= cast(T[])arr[n .. n + m];
}
return result;
}
size_t[] shape(Variant v) {
typeof(return) dims;
while (cast(TypeInfo_Array) v.type !is null) {
dims ~= v.length;
v = v[0];
}
if (!dims.length && v.length) {
dims ~= v.length;
dims ~= 0;
}
return dims;
}
void main() {
foreach(x; 1..100) {
foreach(y; 1..100) {
auto test = Variant(generate!int(x, y));
assert(shape(test) == [x, y]);
}
}
}
```
SDB@79
Re: How to obtain Variant underlying type?
On Monday, 11 July 2022 at 05:41:40 UTC, jfondren wrote:
Oh, sorry. I didn't defend the code in any way because I
assumed that the exceptional design would be seen as obviously
bad (and that someone else would dig harder in order to find a
better solution).
And you were right. I did search for a better solution and came
across [1]. Although I was having some issues adapting it for my
use case, Paul Backus' follow-up clarified the issue. This is
what my naive brain led to before reading this response.
```d
size_t[] shape(Variant v)
{
typeof(return) dims;
while(cast(TypeInfo_Array) v.type !is null) {
dims ~= v.length;
v = v[0];
}
if(!dims.length && v.length) {
dims ~= v.length;
dims ~= 0;
}
return dims;
}
```
Didn't see the bugs that would occur when a scalar or empty array
was passed because I hadn't tested for them.
if (!v.length) break;
Pure gold! Bugs are eliminated, and the code is shorter. Thank
you.
--anonymouse
[1]
https://tastyminerals.github.io/tasty-blog/dlang/2020/03/22/multidimensional_arrays_in_d.html
Re: How to obtain Variant underlying type?
On Sunday, 10 July 2022 at 19:14:34 UTC, Paul Backus wrote:
For reference, this is the more correct way:
```d
while (cast(TypeInfo_Array) v.type !is null) {
Variant elem = v[0];
// etc.
}
```
Hard to blame anyone for not coming up with that on their first
try, especially since `TypeInfo_Array` is not even
documented--you have to read the source of `object.d` to find
out about it.
I honestly cannot say why but I was having a problem using this
earlier. After several hours of frustration, I rebooted the
computer, went for a run, came back, and tried again. It works!!!
Thank you very much.
--anonymouse
Re: How to obtain Variant underlying type?
On Monday, 11 July 2022 at 03:17:33 UTC, anonymouse wrote:
On Sunday, 10 July 2022 at 18:31:46 UTC, drug007 wrote:
I'd like to say that using of exception to break loop is
really bad. Exception is exceptional thing but in the case
above the exception is ordinary completion of the loop happens
on regular basis. Don't do that.
Thanks for the advice. Lesson learned.
--anonymouse
Oh, sorry. I didn't defend the code in any way because I assumed
that the exceptional design would be seen as obviously bad (and
that someone else would dig harder in order to find a better
solution).
The TypeInfo_Array fix breaks the last assertion of those unit
tests, though. This works:
```d
import std.variant : Variant;
size_t[] shape(Variant v) {
size_t[] s;
while (cast(TypeInfo_Array) v.type !is null && v.length > 0) {
Variant elem = v[0];
s ~= v.length;
v = elem;
}
return s;
}
```
Although, that last assertion really is debatable. Languages like
APL would read it as having a shape of [2, 0]:
```d
import std.variant : Variant;
size_t[] shape(Variant v) {
size_t[] s;
while (cast(TypeInfo_Array) v.type !is null) {
s ~= v.length;
if (!v.length) break;
v = v[0];
}
return s;
}
unittest {
assert([3, 1] == [[1], [2], [3]].Variant.shape);
assert([2, 1] == [[1], [2]].Variant.shape);
assert([2, 2] == [[1, 0], [2, 0]].Variant.shape);
assert([2] == [1, 2].Variant.shape);
assert([] == 2.Variant.shape);
assert([2, 0] == [[], []].Variant.shape);
// irregularity not checked
assert([2, 2] == [[1, 0], [2]].Variant.shape);
}
```
Re: How to obtain Variant underlying type?
On Sunday, 10 July 2022 at 18:31:46 UTC, drug007 wrote: I'd like to say that using of exception to break loop is really bad. Exception is exceptional thing but in the case above the exception is ordinary completion of the loop happens on regular basis. Don't do that. Thanks for the advice. Lesson learned. --anonymouse
Re: How to obtain Variant underlying type?
On Sunday, 10 July 2022 at 18:31:46 UTC, drug007 wrote:
On 7/10/22 20:26, anonymouse wrote:
On Sunday, 10 July 2022 at 06:26:37 UTC, jfondren wrote:
```d
import std.variant : Variant;
size_t[] shape(Variant v) {
import std.variant : VariantException;
size_t[] s;
try {
while (true) {
Variant elem = v[0];
s ~= v.length;
v = elem;
}
} catch (VariantException e) {
return s;
}
}
```
Thank you very much.
I'd like to say that using of exception to break loop is really
bad. Exception is exceptional thing but in the case above the
exception is ordinary completion of the loop happens on regular
basis. Don't do that.
For reference, this is the more correct way:
```d
while (cast(TypeInfo_Array) v.type !is null) {
Variant elem = v[0];
// etc.
}
```
Hard to blame anyone for not coming up with that on their first
try, especially since `TypeInfo_Array` is not even
documented--you have to read the source of `object.d` to find out
about it.
Re: How to obtain Variant underlying type?
On Sunday, 10 July 2022 at 06:26:37 UTC, jfondren wrote:
```d
import std.variant : Variant;
size_t[] shape(Variant v) {
import std.variant : VariantException;
size_t[] s;
try {
while (true) {
Variant elem = v[0];
s ~= v.length;
v = elem;
}
} catch (VariantException e) {
return s;
}
}
```
Thank you very much.
Re: How to obtain Variant underlying type?
On Saturday, 9 July 2022 at 23:04:20 UTC, anonymouse wrote:
On Saturday, 9 July 2022 at 14:46:36 UTC, Adam D Ruppe wrote:
Impossible; Variant's type is only known at runtime, and this
would require compile time knowledge.
Hmmm. Okay, thanks. What I really need to know is how many
dimensions an array has and the total elements per dimension so
that I can create temporary storage for it later.
this(T)(T a)
in(imported!"std.traits".isDynamic!T)
{
data = a; // data is of type Variant
shape = [a.length, {?, ...}]; // what's the best way
to deterine?
}
Thanks,
--anonymouse
```d
import std.variant : Variant;
size_t[] shape(Variant v) {
import std.variant : VariantException;
size_t[] s;
try {
while (true) {
Variant elem = v[0];
s ~= v.length;
v = elem;
}
} catch (VariantException e) {
return s;
}
}
unittest {
assert([3, 1] == [[1], [2], [3]].Variant.shape);
assert([2, 1] == [[1], [2]].Variant.shape);
assert([2, 2] == [[1, 0], [2, 0]].Variant.shape);
assert([2] == [1, 2].Variant.shape);
assert([] == 2.Variant.shape);
// irregularity not checked
assert([2, 2] == [[1, 0], [2]].Variant.shape);
// arguably should be [2, 0]
assert([2] == [[], []].Variant.shape);
}
```
Re: How to obtain Variant underlying type?
On Saturday, 9 July 2022 at 14:46:36 UTC, Adam D Ruppe wrote:
Impossible; Variant's type is only known at runtime, and this
would require compile time knowledge.
Hmmm. Okay, thanks. What I really need to know is how many
dimensions an array has and the total elements per dimension so
that I can create temporary storage for it later.
this(T)(T a)
in(imported!"std.traits".isDynamic!T)
{
data = a; // data is of type Variant
shape = [a.length, {?, ...}]; // what's the best way to
deterine?
}
Thanks,
--anonymouse
Re: How to obtain Variant underlying type?
On Saturday, 9 July 2022 at 14:36:44 UTC, anonymouse wrote: auto vb = v.base; // what should I put here to achieve the following: typeof(vb); // int[][] Impossible; Variant's type is only known at runtime, and this would require compile time knowledge.
