How to get type returned by e.g. std.algorithm.iteration.filter

[Christian Köstlin]

On 19.05.19 20:38, Jacob Carlborg wrote:
> On 2019-05-19 15:36, Christian Köstlin wrote:
> 
>> Unfortunately I have no idea how to even store the result of this 
>> search in an attribute of ByMinimum, as I cannot writeout its type.
> 
> In general you can use `typeof(<expression>)`, where `<expression>` is 
> the expression you want to get the type of.
> 
Thanks for the hint. The best I could come up with this is:

#!/usr/bin/env rdmd
import std.stdio;
import std.algorithm;
import std.typecons;
import std.array;
import std.range;
import std.traits;

auto byMinimum(Ranges)(Ranges ranges)
{
     auto getNonEmpty()
     {
         return ranges.filter!("!a.empty");
     }

     auto minimumOfRanges(Ranges)(Ranges ranges) {
         // dfmt off
         return ranges
             .map!(range => tuple!("range", "line")(range, range.front))
             .minElement!("a.line");
         // dfmt on
     }
     auto nonEmpty = getNonEmpty;
     ReturnType!(minimumOfRanges!(typeof(nonEmpty))) minRangeAndLine;
     struct ByMinimum(Ranges)
     {
         bool empty()
         {
             return nonEmpty.empty;
         }

         auto front()
         {
             minRangeAndLine = minimumOfRanges(nonEmpty);
             return minRangeAndLine;
         }

         void popFront()
         {
             minRangeAndLine.range.popFront;
             nonEmpty = getNonEmpty;
         }
     }
     return ByMinimum!(Ranges)();
}

void main(string[] files)
{
     foreach (n; files[1 .. $].map!(name => 
File(name).byLine(No.keepTerminator)).array.byMinimum)
     {
         writeln(n.line);
     }
}


Still it looks a little clumsy. Any ideas?

--
Christian