https://stackoverflow.com/questions/33779822/unable-to-call-each-on-a-lockstep-range-containing-2-or-more-ranges

http://dpaste.dzfl.pl/76c79f1f12ab

void main(){
  import std.container;
  import std.stdio;
  import std.algorithm.iteration;
  import std.range;
  Array!int ai = [1,2,3,4];
  Array!int ai1 = [1,2,3,4];
  Array!int ai2 = [1,2,3,4];

  auto arange = lockstep(ai[],ai1[]);
  arange.each!((a,b) => writeln(a, b));

  auto arange2 = lockstep(ai[],ai1[],ai2[]);
  arange2.each!((a,b,c) => writeln(a, b, c));
}

Error: template std.algorithm.iteration.each cannot deduce function from argument types !((a, b, c) => writeln(a, b, c))(Lockstep!(RangeT!(Array!int), RangeT!(Array!int), RangeT!(Array!int))), candidates are: /opt/compilers/dmd2/include/std/algorithm/iteration.d(820):
std.algorithm.iteration.each(alias pred = "a")


"arange" works but "arange2" doesn't because the compiler is unable to deduce the the function. The error even appears if I explicitly add the argument types.

On Wednesday, 18 November 2015 at 12:20:42 UTC, maik klein wrote:
> https://stackoverflow.com/questions/33779822/unable-to-call-each-on-a-lockstep-range-containing-2-or-more-ranges
>
> http://dpaste.dzfl.pl/76c79f1f12ab
>
> void main(){
>   import std.container;
>   import std.stdio;
>   import std.algorithm.iteration;
>   import std.range;
>   Array!int ai = [1,2,3,4];
>   Array!int ai1 = [1,2,3,4];
>   Array!int ai2 = [1,2,3,4];
>
>   auto arange = lockstep(ai[],ai1[]);
>   arange.each!((a,b) => writeln(a, b));
>
>   auto arange2 = lockstep(ai[],ai1[],ai2[]);
>   arange2.each!((a,b,c) => writeln(a, b, c));
> }
>
> Error: template std.algorithm.iteration.each cannot deduce function from argument types !((a, b, c) => writeln(a, b, c))(Lockstep!(RangeT!(Array!int), RangeT!(Array!int), RangeT!(Array!int))), candidates are: /opt/compilers/dmd2/include/std/algorithm/iteration.d(820):
> std.algorithm.iteration.each(alias pred = "a")
>
>
> "arange" works but "arange2" doesn't because the compiler is unable to deduce the the function. The error even appears if I explicitly add the argument types.

I think this is a bug, please report it at issues.dlang.org and perhaps there will be an explanation or it will be fixed.
In the mean time, something like this should work:

  auto arange2 = zip(ai[],ai1[],ai2[]);

  arange2.each!((t) => writeln(t[0], t[1], t[2]));
  // or if you really must have the names:
  arange2.each!((t) => (a,b,c){ writeln(a, b, c); }(t.expand));

On Wednesday, 18 November 2015 at 13:51:59 UTC, John Colvin wrote:
> On Wednesday, 18 November 2015 at 12:20:42 UTC, maik klein wrote:
>> [...]
>
> I think this is a bug, please report it at issues.dlang.org and perhaps there will be an explanation or it will be fixed.
> In the mean time, something like this should work:
>
>   auto arange2 = zip(ai[],ai1[],ai2[]);
>
>   arange2.each!((t) => writeln(t[0], t[1], t[2]));
>   // or if you really must have the names:
>   arange2.each!((t) => (a,b,c){ writeln(a, b, c); }(t.expand));

Thanks, but the problem I have with zip is that it doesn't work with "ref".


for example

auto arange3 = zip(ai[],ai1[],ai2[]);
foreach(ref a; arange3){
  a[0] = 42;
}
Won't change anything. Is this another bug?

On Wednesday, 18 November 2015 at 14:11:45 UTC, maik klein wrote:
> On Wednesday, 18 November 2015 at 13:51:59 UTC, John Colvin wrote:
>> On Wednesday, 18 November 2015 at 12:20:42 UTC, maik klein wrote:
>>> [...]
>>
>> I think this is a bug, please report it at issues.dlang.org and perhaps there will be an explanation or it will be fixed.
>> In the mean time, something like this should work:
>>
>>   auto arange2 = zip(ai[],ai1[],ai2[]);
>>
>>   arange2.each!((t) => writeln(t[0], t[1], t[2]));
>>   // or if you really must have the names:
>>   arange2.each!((t) => (a,b,c){ writeln(a, b, c); }(t.expand));
>
> Thanks, but the problem I have with zip is that it doesn't work with "ref".
>
>
> for example
>
> auto arange3 = zip(ai[],ai1[],ai2[]);
> foreach(ref a; arange3){
>   a[0] = 42;
> }
> Won't change anything. Is this another bug?

Unfortunately, yes: https://issues.dlang.org/show_bug.cgi?id=10541

Note that

while(!arange3.empty)
{
    arange3.front[0] = 42;
    arange3.popFront();
}

should work as expected.

On Wednesday, 18 November 2015 at 12:20:42 UTC, maik klein wrote:
> https://stackoverflow.com/questions/33779822/unable-to-call-each-on-a-lockstep-range-containing-2-or-more-ranges
>
> http://dpaste.dzfl.pl/76c79f1f12ab
>
> void main(){
>   import std.container;
>   import std.stdio;
>   import std.algorithm.iteration;
>   import std.range;
>   Array!int ai = [1,2,3,4];
>   Array!int ai1 = [1,2,3,4];
>   Array!int ai2 = [1,2,3,4];
>
>   auto arange = lockstep(ai[],ai1[]);
>   arange.each!((a,b) => writeln(a, b));
>
>   auto arange2 = lockstep(ai[],ai1[],ai2[]);
>   arange2.each!((a,b,c) => writeln(a, b, c));
> }
>
> Error: template std.algorithm.iteration.each cannot deduce function from argument types !((a, b, c) => writeln(a, b, c))(Lockstep!(RangeT!(Array!int), RangeT!(Array!int), RangeT!(Array!int))), candidates are: /opt/compilers/dmd2/include/std/algorithm/iteration.d(820):
> std.algorithm.iteration.each(alias pred = "a")
>
>
> "arange" works but "arange2" doesn't because the compiler is unable to deduce the the function. The error even appears if I explicitly add the argument types.

Which version of the compiler are you using?

On Wednesday, 18 November 2015 at 17:22:52 UTC, Meta wrote:
> On Wednesday, 18 November 2015 at 12:20:42 UTC, maik klein wrote:
>> [...]
>
> Which version of the compiler are you using?
Linux - DMD64 D Compiler v2.069.0

On Wednesday, 18 November 2015 at 17:40:21 UTC, maik klein wrote:
> On Wednesday, 18 November 2015 at 17:22:52 UTC, Meta wrote:
>>
>> Which version of the compiler are you using?
> Linux - DMD64 D Compiler v2.069.0

https://issues.dlang.org/show_bug.cgi?id=15357
https://issues.dlang.org/show_bug.cgi?id=15358