struct S(T) {
  T[] data;

  int opApply(int delegate (T*) dg) {
    for(size_t i = 0; i < data.length; i++) {
      int result = dg(&data[i]);
      if(result != 0)
        return result;
    }

    return 0;
  }

  int opApply(int delegate (const T*) dg) const {
    for(size_t i = 0; i < data.length; i++) {
      int result = dg(&data[i]);
      if(result != 0)
        return result;
    }

    return 0;
  }

  int opApply(int delegate (size_t, T*) dg) {
    for(size_t i = 0; i < data.length; i++) {
      int result = dg(i, &data[i]);
      if(result != 0)
        return result;
    }

    return 0;
  }

  int opApply(int delegate (size_t, const T*) dg) const {
    for(size_t i = 0; i < data.length; i++) {
      int result = dg(i, &data[i]);
      if(result != 0)
        return result;
    }

    return 0;
  }
}

void main() {
  auto s1 = S!int([0, 1, 2, 3]);
  auto s2 = const S!int([0, 1, 2, 3]);

  import std.stdio : writeln, writefln;
  writeln("S!int, 1 arg:");
  foreach(s; s1)
    (*s)++;

  writeln("S!int, 2 args:");
  foreach(i, s; s1)
    writefln("%s: %s", i, *s);

  writeln("const S!int, 1 arg:");
  foreach(s; s2)
    writeln(*s);

  writeln("const S!int, 2 args:");
  foreach(i, s; s2)
    writefln("%s: %s", i, *s);
}