Hello! I'm trying to make a deepMap function which operates on the deepest non-range element of an array. I think that this function should theoretically work, however there are some compiler errors that I can't quite understand.

Here's the code: http://dpaste.dzfl.pl/97918311

And the compiler error because DPaste's compiler service seems to be offline:

src\algorithm_util.d(26): Error: function algorithm_util.__unittestL34_5.deepMap!(__lambda4, int[]).deepMap is a nested function and cannot be accessed from algorithm_util.__unittestL34_5.deepMap!(__lambda4, int[][]).deepMap.__lambda2300!(int[]).__lambda2300DMD
v2.064 DEBUG

deepMap works just fine if I pass in an array that isn't nested, so this will work:

	auto a = [1, 2, 3];
	auto b = a.deepMap!(a => a + 1)();
	writeln(b);
	// "[2, 3, 4]"

Can someone explain what is going on?

Thank you,
Dylan Knutson

On 06/12/2013 03:45 PM, Dylan Knutson wrote:
> Hello! I'm trying to make a deepMap function which operates on the
> deepest non-range element of an array. I think that this function should
> theoretically work, however there are some compiler errors that I can't
> quite understand.
>
> Here's the code: http://dpaste.dzfl.pl/97918311
>
> And the compiler error because DPaste's compiler service seems to be
> offline:
>
> src\algorithm_util.d(26): Error: function
> algorithm_util.__unittestL34_5.deepMap!(__lambda4, int[]).deepMap is a
> nested function and cannot be accessed from
> algorithm_util.__unittestL34_5.deepMap!(__lambda4,
> int[][]).deepMap.__lambda2300!(int[]).__lambda2300DMD
> v2.064 DEBUG
>
> deepMap works just fine if I pass in an array that isn't nested, so this
> will work:
>
>      auto a = [1, 2, 3];
>      auto b = a.deepMap!(a => a + 1)();
>      writeln(b);
>      // "[2, 3, 4]"
>
> Can someone explain what is going on?
>
> Thank you,
> Dylan Knutson

Perhaps this limitation:

  http://d.puremagic.com/issues/show_bug.cgi?id=5710

Ali

DPaste has stopped responding to requests at the time of writing, so here's the code in case its still down by the time someone reads this:


----
import std.algorithm : map;
import std.range : isInputRange, ElementType;

// Doesn't work
//template deepMap(alias pred, Range)
//if(isInputRange!Range)
//{
//	static if(isInputRange!(ElementType!Range))
//	{
//		alias deepMap = map!(a => deepMap!(pred, typeof(a))(a));
//	}
//	else
//	{
//		alias deepMap = map!(pred);
//	}
//}

// Neither does this, for the same reason
auto deepMap(alias pred, Range)(Range r)
if(isInputRange!Range)
{
	static if(isInputRange!(ElementType!Range))
	{
		return r.map!( a => a.deepMap!(pred)() )();
	}
	else
	{
		return r.map!(pred)();
	}
}

unittest {
	import std.stdio;

	auto a = [[1, 1], [1, 1]];
	auto b = a.deepMap!(a => a + 1)();
	writeln(b);
	//assert(b == [[2, 2], [2, 2]]);
}

----

On 06/12/2013 03:49 PM, Dylan Knutson wrote:

> DPaste has stopped responding to requests at the time of writing,

Being an old ;) old-timer I never understood the need for those sites.

> ----
> import std.algorithm : map;
> import std.range : isInputRange, ElementType;

As a workaround, make that lambda a free-standing function here:

auto intermediate(T, alias pred)(T a)
{
    return a.deepMap!(pred)();
}

> // Neither does this, for the same reason
> auto deepMap(alias pred, Range)(Range r)
> if(isInputRange!Range)
> {
>      static if(isInputRange!(ElementType!Range))
>      {
>          return r.map!( a => a.deepMap!(pred)() )();

And use that free-standing instead:

        return r.map!(intermediate!(ElementType!Range, pred))();

Ali