Read-only properties in C# 3.0 object initialization

Question

If I have the following code:

public class MyClass 
{ 
  public string myName { get; private set; } 
  public string myId { get; set; } 
}

A private compiler-generated variable is created for the setter. I want the setter not to be accessible for object initialization only. But, how do I get to initially set the myName variable?

Reading about object initialization I found the following:

... it’s read-only and the private field representing the underlying storage has a compiler-generated name that we cannot use in a constructor to assign to it. The solution is to use [...] object initializers

The solution would be, then, to use:

MyClass mc = new MyClass { 
myName = "What ever", 
myId = "1234" 
};

But this ends up in a compiler error sayin that:

The property or indexer 'MyClass.MyClass.myName' cannot be used in this context because the set accessor is inaccessible

So, is there a way to achieve setting this value using object initialization? If there is, what is the correct way to do it?

Answer 1

No there is no way to achieve this. Object Initializers only allow you to access fields and properties which would be otherwise accessible outside the initializer.

Your best option is to use a constructor which explicitly sets these properties.

Answer 2

If they need to be set at initialisation then consider passing them as args to the constructor

Answer 3

I've had this requirement int the past as well for OR/M stuff. What I basically do is use a real property with backer field and check to see if the property has already been set. If so, throw an exception.

public string myName
{
    get{ return _myName; }
    set
    {
     if( _myName != null && _myName != value )
      throw new Exception( "The myName property may only be set once." );
     _myName = value;
    }
}

private string _myName;

And another option for OR/M compatibility that also takes advantage of constructor initialization:

public class MyClass 
{ 
 [Obsolete( "For ORM use only!" )] 
 [EditorBrowsableState( EditorBrowsableState.Never )]
 public MyClass(){}

 public MyClass( string name ){ myName = name; }

 public string myName { get; private set; } 
 public string myId { get; set; } 
}

Answer 4

Private set on myName means you can only initialize (set) it from something that is a member of MyClass. For example:

     public class MyClass {
  public string myName { get; private set; }
  public string myId { get; set; }

  public static MyClass GetSampleObject() {
   MyClass mc = new MyClass
   {
    myName = "Whatever",
    myId = "1234"
   };
   return mc;
  }
 }

(I copied and pasted your initialization code into the GetSampleObject method).

But if you try to set it outside MyClass, you get a compiler error, because private is private.