readonly member (but assignable at constructor time)

[Dr.No via Digitalmars-d-learn]

In C# you can have a readonly member assignable either at 
declaration or constructor time, like this:

class C
{
  readonly myClass mc;
  this()
  {
    mc = new myClass();
  }


  void doSomething()
  {
    mc = new myClass(); // wrong! result in compiler error, mc is 
readonly
  }
}

Does D have something like this natively or there's a way to do 
so with traits/CTFE at runtime?