For fun: Expressive C++ 17 Coding Challenge in D

[lithium iodate]

On Wednesday, 4 October 2017 at 15:30:08 UTC, Ali Çehreli wrote:
> the hidden \r characters at the ends

Those got me too!


Here's my less than optimal solution:

int main(string[] args)
{   import std.stdio;
     import std.algorithm.iteration : map, splitter, joiner, each;
     import std.algorithm.searching : countUntil;
     import std.range : enumerate;
     import std.string : chomp;

     if (args.length != 5 && args.length != 4)
     {   stderr.writeln("Something went wrong and it's obviously 
your fault.");
         return 1;
     }

     immutable columnID = args[2];
     immutable substitute = args[3];

     auto data = File(args[1], "r").byLine.map!chomp;
     if (data.empty)
     {   stderr.writeln("input file missing\n\n(actually it 
exists, it's just "
                 ~ "empty)\n\n(your fault regardless)");
         return 1;
     }

     File output;
     if (args.length == 5)
         output = File(args[4], "w");
     else
         output = stdout;

     immutable matchedColumn = 
data.front.splitter(",").countUntil(columnID);
     if (matchedColumn < 0)
     {   stderr.writeln("column name doesn’t exist in the input 
file\n\n(and "
                 ~ "it's your fault)");
         return 1;
     }

     output.writeln(data.front);
     data.popFront;

     data.map!(line => line
             .splitter(",")
             .enumerate
             .map!(a => a.index == matchedColumn ? substitute : 
a.value)
             .joiner(",")).each!(a => output.writeln(a));

     return 0;
}

I think the biggest problem is the lack of support for quoted 
content.