Public fields and properties are not compatible

If your class wants to expose some data, you have two possibilities:

1. Use a public field
   

   public class Person 
   {
       public string Name;
   } 

2. Use a public property that is backed by a private field
   

   public class Person 
   {
       private string name;
   
       public string Name 
       {
           get
           {
               return name;
           }
           set
           {
               name = value;
           }
       }
   }

The general advise is that you should not have any public fields, thus you should always use properties. However some people suggest that you can start out with a public field and that you can easily change it into a property when the need arises.

But this is not true for two reasons:

1. A public field and a property are binary incompatible. When you change your public field into a property you will have to recompile all the clients of your class.
2. A public field and a propery are also incompatible at source-code level. A public field can be passed as a ref- or out-parameter while a property cannot. So when you change your public field into a property, you may have to actually change the client code which may not be a trivial task.

So my advise: unless you have *very* strict performance considerations always use properties.

Regarding performance, keep in mind that a simple propery that is not marked as virtual (or that is part of a sealed class) will likely be inlined by the compiler so there shouldn't be any performance impact at all (in release-builds).

Kristof.