D言語でTemplate Meta Programmingを駆使して書いた、任意の深さのnested forを生成するテンプレート

forTemplate.d

import std.stdio;

template FOR(alias func, alias cond) {
  import std.algorithm,
         std.traits,
         std.range,
         std.conv;

  void FOR() {
    immutable lambdaStr = (lamArgs =>
      (temp) {
        foreach(e; lamArgs) {
          temp ~= "for(ulong " ~ e ~ "; " ~ "cond(" ~ e ~ "); " ~ e ~ "++)";
        }

        return temp ~ "func(" ~ lamArgs.join(", ") ~ ");";
      }("")
    )(arity!func.iota.map!(i => "arg" ~ i.to!string));

    mixin(lambdaStr);
  }
}

void main() {
  FOR!((ulong i1, ulong i2) => writeln(i1 * i2), i => i < 4);
}