Is read-only auto-implemented property possible?

Question

I found a topic on MSDN that talks that yes, this is possible.

I did a test that seems to break this statement:

using System;  namespace Test {     class Program     {         static void Main(string[] args)         {             Foo f = new Foo("1");             Console.WriteLine(f.Bar); // prints 1             f.Test("2");             Console.WriteLine(f.Bar);// successfully prints 2         }     }      class Foo     {         public Foo(string b)         {             this.Bar = b;         }          public string Bar { get; private set; }          public void Test(string b)         {             // this would be impossible for readonly field!             // next error would be occur: CS0191 or CS0191             // A readonly field cannot be assigned to (except in a constructor or a variable initializer)             this.Bar = b;          }     } } 

Where am I wrong?

Answer 1

The answer below was written back in 2010. In C# 6 (released in 2015) you can write read-only automatically-implemented properties:

// This can only be assigned to in a constructor public int Foo { get; } 

---

You're absolutely right. Properly read-only automatically implemented properties are currently impossible. Making the setter private isn't the same thing, regardless of what some books and MSDN might say :)

If I ruled the world, this would not be the case. When I see some of the language designers at NDC 2010 in June (please come along!) I intend to try to persuade, bribe, cajole and generally make a nuisance of myself until they agree. It's just one wafer-thin feature, after all.

Looking at that MSDN article, the text itself doesn't say that it creates a read-only automatic property. It creates an immutable type using an automatic property, and that's correct. The only problematic bits are the comments saying

// Read-only properties. 

... which are definitely wrong. The framework agrees with us:

var prop = typeof(Contact).GetProperty("Name"); Console.WriteLine(prop.CanWrite); // Prints True 

Answer 2

The property is read-only outside the Foo class. I think that's what article is getting at.

But it's not the same as marking a variable with the readonly keyword.