Runtime O(1) FizzBuzz by nested string-mixin

rt_o1_fizzbuzz.d

import std.stdio;
import std.format;
import std.traits;
import std.array;

mixin(q{
  enum string fizzbuzz_code = {
    enum string prim_fb(int M)() {
      static if (M % 15 == 0) { return "writeln(\"fizzbuzz\");"; }
      else   if (M % 3 == 0)  { return "writeln(\"fizz\");"; }
      else   if (M % 5 == 0)  { return "writeln(\"buzz\");"; }
      else                    { return "writeln(\"%d\");".format(M); }
    }
    enum string[] gen_fb_code(int M, int t = 0, string[] tmp = [])() {
      static if (M == t) {
        return tmp;
      } else {
        return gen_fb_code!(M, t + 1, tmp ~ prim_fb!(t));
      }
    }

    enum string header = "void fizzbuzz() {";
    enum string footer = "}";

    return header ~ gen_fb_code!(N).join("\n") ~ footer;
  }();

  mixin(fizzbuzz_code);
});

enum N = 30;

void main() {
  fizzbuzz();
}