chunkBy limitation?
I wondered if this is a current limitation of chunkBy
implementation:
// http://dpaste.dzfl.pl/52d6a0c5d0ab
void bar(int[] foo)
{
bool less(int a, int b) // contrived
{
return a < b;
};
foo.sort!less.groupBy;
}
resulting in:
/opt/compilers/dmd2/include/std/algorithm/iteration.d(1529):
Error: function f351.bar.SortedRange!(int[],
less).SortedRange.groupBy!().groupBy.ChunkByImpl!(__lambda1,
int[]).ChunkByImpl.Group.popFront cannot access frame of function
f351.bar.SortedRange!(int[], less).SortedRange.groupBy!().groupBy
...
I can see that the implementation of chunkBy is nested:
struct ChunkByImpl
{
static struct Group {}
}
and that the predicate (less in this case) is accessed from the
nested struct Group which is, probably, what's causing the
compilation error.
The question is if this is an implementation error (i.e. Group
should probably be moved to the top level) or a compiler issue?
Thanks in advance.
Re: chunkBy limitation?
On 10/02/2015 02:21 AM, Dmitri wrote:
> I wondered if this is a current limitation of chunkBy implementation:
>
> // http://dpaste.dzfl.pl/52d6a0c5d0ab
> void bar(int[] foo)
> {
> bool less(int a, int b) // contrived
> {
> return a < b;
> };
>
> foo.sort!less.groupBy;
> }
>
> resulting in:
>
> /opt/compilers/dmd2/include/std/algorithm/iteration.d(1529): Error:
> function f351.bar.SortedRange!(int[],
> less).SortedRange.groupBy!().groupBy.ChunkByImpl!(__lambda1,
> int[]).ChunkByImpl.Group.popFront cannot access frame of function
> f351.bar.SortedRange!(int[], less).SortedRange.groupBy!().groupBy
> ...
>
> I can see that the implementation of chunkBy is nested:
> struct ChunkByImpl
> {
> static struct Group {}
> }
>
> and that the predicate (less in this case) is accessed from the nested
> struct Group which is, probably, what's causing the compilation error.
>
> The question is if this is an implementation error (i.e. Group should
> probably be moved to the top level) or a compiler issue?
>
> Thanks in advance.
This is a known D issue. Currently, objects have a single context
pointer. Here is a bug discussion about it:
https://issues.dlang.org/show_bug.cgi?id=5710
A workaround for your example is making less() static, which removes its
context pointer:
void bar(int[] foo)
{
import std.algorithm : sort;
static bool less(int a, int b) // contrived
{
return a < b;
}
foo.sort!less.groupBy;
}
void main() {}
I've just realized that I don't know how to handle the case where less()
really needs some other state (e.g. it may need to use a local variable
in main). What can we do?
Ali
Re: chunkBy limitation?
On Friday, 2 October 2015 at 18:16:59 UTC, Ali Çehreli wrote:
On 10/02/2015 02:21 AM, Dmitri wrote:
> [...]
implementation:
> [...]
Error:
> [...]
function
> [...]
less).SortedRange.groupBy!().groupBy
> [...]
the nested
> [...]
compilation error.
> [...]
Group should
> [...]
This is a known D issue. Currently, objects have a single
context pointer. Here is a bug discussion about it:
https://issues.dlang.org/show_bug.cgi?id=5710
A workaround for your example is making less() static, which
removes its context pointer:
void bar(int[] foo)
{
import std.algorithm : sort;
static bool less(int a, int b) // contrived
{
return a < b;
}
foo.sort!less.groupBy;
}
void main() {}
I've just realized that I don't know how to handle the case
where less() really needs some other state (e.g. it may need to
use a local variable in main). What can we do?
Ali
Thanks, Ali - this is helpful. The problem was figuring out what
exactly is wrong given a bunch of unhelpful error messages. A
somewhat better message comes when using a unary predicate
version of chunkBy.
