On Wednesday, 11 July 2018 at 08:31:30 UTC, Dorian Haglund wrote:
Hi.
I'm trying to use taskPool.reduce with a delegate, for example:
import std.parallelism;
int main(string[] args)
{
int f(int a, int b)
{
if (args.length > 1)
return a+b;
else
return a-b;
}
auto res = taskPool.reduce!f([1, 2, 3]);
return 0;
}
But it fails to compile (with gdc 8.1.0, dmd v2.081)
complaining that
template instance reduce!(f) cannot use local 'f' as parameter
to non-global template reduce(functions...)
The snippet above compiles with the reduce function from
std.algorithm.
Is there a way to make the code compile with taskPool.reduce ?
(I don't want to write two functions and choosing one depending
on args.length)
Why the interface difference between std.algorithm's reduce and
taskPool.reduce ?
Best regards,
Dorian
As the error message says taskPool.reduce is a non-global
template. It's embedded in a taskPool struct. I can't say what
the reason is that a delegate cannot be used with such a
template. I'd be interested in hearing what the reason is.
(See Paul's reply).
I'm trying to trick around it, but can't get this to work...
https://run.dlang.io/is/EGbtuq
import std.parallelism;
int main(string[] args)
{
static int f(bool cond)(int a, int b)
{
static if (cond)
return a+b;
else
return a-b;
}
template getF(alias func)
{
auto getF(T)(T arg)
{
if (args.length > 1)
return func!(f!true)(arg); // line 18
else
return func!(f!false)(arg); // line 20
}
}
auto res = getF!(taskPool.reduce)([1,2,3]);
return 0;
}
onlineapp.d(18): Error: need this for reduce of type @system
int(int[] _param_0)
onlineapp.d(20): Error: need this for reduce of type @system
int(int[] _param_0)
