Hi again,

I have this simple toy code :

import point;
import std.random;
import std.algorithm;
import std.functional;

void getRandomPoint(R)(R randVar, ref Point p)
{
      p.x = randVar;
      p.y = randVar;
      p.z = randVar;
}

void main()
{
      Point[500] points;
      auto randVar = uniform(0.0f, 1.0f);

      alias test = partial!(getRandomPoint, randVar);

      points.map!(test);
}

And get the following error :

kmeans_example.d(79): Error: template std.algorithm.iteration.map
cannot deduce function from argument types
!(partial)(Point[500]), candidates are:
/usr/include/dmd/phobos/std/algorithm/iteration.d(434):
std.algorithm.iteration.map(fun...) if (fun.length >= 1)

Btw, I don't understand why :

auto test = partial!(getRandomPoint, randVar);

dont work...partial doesnt return a delegate it seems...:/

(it's not on line 79 obviously, you got me :D)

On Monday, 30 March 2015 at 18:07:18 UTC, matovitch wrote:
> kmeans_example.d(79): Error: template std.algorithm.iteration.map

That error is easy: use points[].map!(test) instead of points.map.

Since points is a static array, it isn't a range. Static arrays can't be popped through. But if you slice it, then it yields a usable range for map.


The other problem though is the partial!(). It expects a template argument for the thing so it can make a new function right there at compile time... which doesn't work with a runtime variable.

The way I'd do it is just with a little hand written delegate. This will compile, for example:

      auto test = (ref Point p) => getRandomPoint(randVar, p);
      points[].map!(test);


and should do what you need.

On Monday, 30 March 2015 at 18:23:32 UTC, Adam D. Ruppe wrote:
> On Monday, 30 March 2015 at 18:07:18 UTC, matovitch wrote:
>> kmeans_example.d(79): Error: template std.algorithm.iteration.map
>
> That error is easy: use points[].map!(test) instead of points.map.
>
> Since points is a static array, it isn't a range. Static arrays can't be popped through. But if you slice it, then it yields a usable range for map.
>
>
> The other problem though is the partial!(). It expects a template argument for the thing so it can make a new function right there at compile time... which doesn't work with a runtime variable.
>
> The way I'd do it is just with a little hand written delegate. This will compile, for example:
>
>       auto test = (ref Point p) => getRandomPoint(randVar, p);
>       points[].map!(test);
>
>
> and should do what you need.

Nice ! Thanks for the tip ! I tried importing std.range and points.array works too.

On Monday, 30 March 2015 at 18:29:32 UTC, matovitch wrote:
> I tried importing std.range and points.array works too.

Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.

On Monday, 30 March 2015 at 18:34:19 UTC, Adam D. Ruppe wrote:
> On Monday, 30 March 2015 at 18:29:32 UTC, matovitch wrote:
>> I tried importing std.range and points.array works too.
>
> Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.

I was going to ask you the question does it just add the range shell or does it make a copy ? :/ Maybe someone else know.

Well I have a bit of a similar problem with foreach.

If I use classic T[] range, I can do :

foreach(int i, auto t, myRange)...

But if I use an Array!T (from std.container) I get :

cannot infer argument types, expected 1 argument, not 2

Even if I add the brackets []. Any idea ? Thanks for your help ! :)

On Monday, 30 March 2015 at 18:37:53 UTC, matovitch wrote:
> On Monday, 30 March 2015 at 18:34:19 UTC, Adam D. Ruppe wrote:
[...]
>> Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.
>
> I was going to ask you the question does it just add the range shell or does it make a copy ? :/ Maybe someone else know.

Let's check the documentation. http://dlang.org/phobos/std_array.html#array says: "Allocates an array and initializes it with copies of the elements of range r." Documentation says copy.

Let's check the actual behaviour.
----
void main()
{
	int[1] a = [1];
	import std.array: array;
	a.array[0] = 2;
	import std.stdio: writeln;
	writeln(a[0]);
}
----
(also at <http://dpaste.dzfl.pl/1191144a9acf>)
This program prints "1". That's the output we'd expect when `array` makes a copy. Actual behaviour says copy.

So, copy.

On Monday, 30 March 2015 at 19:08:24 UTC, anonymous wrote:
> On Monday, 30 March 2015 at 18:37:53 UTC, matovitch wrote:
>> On Monday, 30 March 2015 at 18:34:19 UTC, Adam D. Ruppe wrote:
> [...]
>>> Aye, that would work too, but the slice I think is more efficient as I'm pretty sure... not completely sure, but I think .array makes a copy of static arrays, whereas the slice doesn't.
>>
>> I was going to ask you the question does it just add the range shell or does it make a copy ? :/ Maybe someone else know.
>
> Let's check the documentation. http://dlang.org/phobos/std_array.html#array says: "Allocates an array and initializes it with copies of the elements of range r." Documentation says copy.
>
> Let's check the actual behaviour.
> ----
> void main()
> {
> 	int[1] a = [1];
> 	import std.array: array;
> 	a.array[0] = 2;
> 	import std.stdio: writeln;
> 	writeln(a[0]);
> }
> ----
> (also at <http://dpaste.dzfl.pl/1191144a9acf>)
> This program prints "1". That's the output we'd expect when `array` makes a copy. Actual behaviour says copy.
>
> So, copy.

That settle the point for array as for [] ? I guess the documentation should have something to say about it too. ;)

On Monday, 30 March 2015 at 19:11:10 UTC, matovitch wrote:
> That settle the point for array as for [] ?

I though that was clear. [] doesn't copy.

> I guess the documentation should have something to say about it too. ;)

hopefully