Why .dup not work with multidimensional arrays?

[Dennis Ritchie via Digitalmars-d-learn]

On Friday, 8 May 2015 at 06:30:46 UTC, Ali Çehreli wrote:
> In D, everything is possible and very easy. :p I called it 
> deepDup:
>
> import std.stdio;
> import std.traits;
> import std.range;
> import std.algorithm;
>
> auto deepDup(A)(A arr)
>     if (isArray!A)
> {
>     static if (isArray!(ElementType!A)) {
>         return arr.map!(a => a.deepDup).array;
>
>     } else {
>         return arr.dup;
>     }
> }
>
> void main()
> {
>     auto c = [[[1, 2, 3], [4, 5, 6, 7, 8]],
>           [[9, 10], [11, 12, 13]]];
>
>     auto d = c.deepDup;
>
>     d[0][1][1 .. $ - 1] *= 3;
>
>     writeln("c = ", c);
>     // [[[1, 2, 3], [4, 5, 6, 7, 8]],
>     //  [[9, 10], [11, 12, 13]]] // OK
>     writeln("d = ", d);
>     // [[[1, 2, 3], [4, 15, 18, 21, 8]],
>     //  [[9, 10], [11, 12, 13]]] // OK
> }
>
> Ali

Thank you. In D it's really easy :)
Recursion, which works with the lambda map looks fine.


I was a little question: why static int idx variable declared 
within a function deepDup takes the values 1, 1, 1, 2, 2, 3, 4, 
as opposed to a global variable static int idx, which receives 
the expected value of 1, 2, 3, 4, 5, 6, 7 ?

-----
import std.stdio,
        std.range,
        std.traits,
        std.algorithm;

// static int idx; // 1, 2, 3, 4, 5, 6, 7 // OK

auto deepDup(A)(A arr)
	if (isArray!A)
{
	static int idx; // 1, 1, 1, 2, 2, 3, 4 // Why is this happening?
	++idx;
	writeln("visited");
	static if (isArray!(ElementType!A)) {
		writeln("ifIdx = ", idx);
		writeln("ifArr = ", arr);
		return arr.map!(a => a.deepDup).array;

	} else {
		writeln("elseIdx = ", idx);
		writeln("elseArr = ", arr);
		return arr.dup;
	}
}

void main() {

	auto a = [[[1, 2, 3], [4, 5, 6, 7, 8]],
		  [[9, 10], [11, 12, 13]]];

	auto b = a.deepDup;

	b[0][1][1 .. $ - 1] *= 3;

	writeln("\nResualt: ");

	writeln("a = ", a);
	// [[[1, 2, 3], [4, 5, 6, 7, 8]],
	//  [[9, 10], [11, 12, 13]]]
	writeln("b = ", b);
	// [[[1, 2, 3], [4, 15, 18, 21, 8]],
	//  [[9, 10], [11, 12, 13]]]
}
-----
http://ideone.com/mAHZyO