Coming from a C++ background, I'm used to sticking the const keyword into function definitions to make objects being passed in read-only values. However, I've found out that this is not possible in C# (please correct me if I'm wrong). After some Googling, I arrived at the conclusion that the only way to make a read-only object is to write an interface that only has 'get' properties and pass that in instead. Elegant, I must say.

public interface IFoo
{
  IMyValInterface MyVal{ get; }
}

public class Foo : IFoo
{
  private ConcreteMyVal _myVal;

  public IMyValInterface MyVal
  {
    get { return _myVal; }
  }
}

I would pass it into:

public void SomeFunction(IFoo fooVar)
{
  // Cannot modify fooVar, Excellent!!
}

This is fine. However, in the rest of my code, I would like to modify my object normally. Adding a 'set' property to the interface would break my read-only restriction. I can add a 'set' property to Foo (and not IFoo), but the signature expects an interface rather than a concrete object. I would have to do some casting.

// Add this to class Foo. Might assign null if cast fails??
set { _myVal = value as ConcreteMyVal; }

// Somewhere else in the code...
IFoo myFoo = new Foo;
(myFoo as Foo).MyFoo = new ConcreteMyVal();

Is there a more elegant way of replicating const or making read-only function parameters without adding another property or a function?