Operator Oveloading (compared with http://qiita.com/szktty/items/9fa3b972fbdae7aaa0ef)

opIndexTut.d

import std.stdio : writeln;

class Company
{
  Employee[] employees;

  auto opOpAssign(string op)(Employee employee) if (op == "~")
  {
    employees ~= employee;
  }

  string opIndex(ulong id)
  {
    foreach (e; employees) if (e.id == id) return e.name;
    throw new Exception("Not found entry.");
  }

  void opIndexAssign(string name, ulong id)
  {
    foreach (ref e; employees) {
      if (e.id == id) {
        e.name = name;
        return;
      }
    }
    throw new Exception("Not found entry.");
  }
}

class Employee
{
  ulong id;
  string name;

  this(typeof(this.tupleof) xs)
  {
    this.tupleof = xs;
  }
}

version(unittest){}
else
void main()
{
  auto company = new Company;
  foreach (i, name; ["kubo38", "kubo39", "kubo40"]) company ~= new Employee(i, name);
  company[1].writeln;
  company[1] = "unko";
  company[1].writeln;
}