Can I make a variable public and readonly (outside where was declared) at same time?

[AsmMan via Digitalmars-d-learn]

I know I can combine it by making an extra variable plus a 
property like this:

class Foo
{
   private int a_;

   void do_something1()
   {
     a_ = baa();
   }

   void do_something2()
   {
     if(cond) a_ = baa2();
   }

   @property int a()
   {
       return a;
    }
}

This is the C#'s to do which I'm translated to D within my 
limited knowledge. I don't do much OOP, maybe it's possible and I 
don't know. I'm using @property to make 'a' accessible and 
readonly at same time but I wanted to do that without this a_ 
extra variable, i.e, only the methods within the Foo class can 
assign a new value to a but a instance of Foo can't. An imaginary 
code example:

class Foo
{
   public MAGIC_HERE int a;

   void do_something1()
   {
     a = baa();
   }

   void do_something2()
   {
     if(cond) a = baa2();
   }
}


And then:

Foo f = new Foo();
writeln(f.a); // output value of a
f.a = 10; // compile error: a is readonly outside Foo's methods.

I hope it's clear (sorry for por English)