On Wed, 13 Oct 2010 18:06:15 +0000, Lars T. Kyllingstad wrote:
> On Wed, 13 Oct 2010 16:46:09 +0000, Nick Treleaven wrote:
>
>> Hi,
>> I'm new to D2 ranges but have been following D for some time. I'm
>> posting here because I want to check if I'm doing anything wrong before
>> filing a bug.
>>
>> The code below is a test case I made after hitting the problem in real
>> code. Basically the pyramid recursive function should print out: [1, 2,
>> 3]
>> [1, 2]
>> [1]
>>
>> This works fine when calling with an int[] range, but calling with
>> SList!int seems to make the compiler hang, eating up memory.
>>
>> Should I file a bug?
>>
>>
>> import std.stdio;
>> import std.range;
>> import std.container;
>>
>> void pyramid(Range)(Range items)
>> {
>> if (items.empty)
>> return;
>> writeln(items);
>> auto len = walkLength(items);
>> auto r = take(items, len - 1);
>> pyramid(r);
>> }
>>
>> void main()
>> {
>> /* array version is fine */
>> int[] arr = [1, 2, 3];
>> pyramid(arr[]);
>>
>> SList!int list = [1, 2, 3];
>> pyramid(list[]); /* infinite loop with dmd 2.049 */
>> }
>
>
> You are creating an infinite recursion of templates. For an array the
> return type of take() is the same array type. For other ranges, the
> return type of take() is Take!Range. So when you instantiate pyramid!
> Range, it instantiates pyramid!(Take!Range), and then
> pyramid!(Take!(Take! Range)), and so on ad infinitum.
>
> A solution could be to make take!(Take!Range)() just return another
> Take! Range. I can look into that, but you should file a bug report on
> it so it's not forgotten.
>
> -Lars
http://d.puremagic.com/issues/show_bug.cgi?id=5052
