Hiding implementation of value types in .NET/C#

No, there isn't. Not globally. However you can make a base class, like:

 public class BaseEntity { public int Id { get; set; } } 

Then derive all of your objects from there:

 public class MyItem : BaseEntity { } 

Then you'd only change your type in one place.

You can create an alias for a type, but you need to define it on every module, can't be done globally:

 using MyIdType = System.Int32; 

Documentation for aliasing is here

That said: I don't think it's good practice to change these kind of things around... think twice, code once.

What about inheritance?

public class UniqueIdentifiedObject { public Guid Id { get; set; } } public class User : UniqueIdentifiedObject { // You don't need to stupidly repeat yourself (DRY) } 

If you can't use inheritance because you've already derived these classes from who know what other class... Then you can use generics:

public class User<TId> where TId : IEquatable<TId> { public TId Id { get; set; } } public class Employee<TId> where TId : IEquatable<TId> { public TId Id { get; set; } } 

This means that you'll need to provide the type of the whole unique identifier during your class instantiations:

Employee<Guid> employee = new Employee<Guid>(); 

I believe generics gets closer to what you're looking for, because it allows you to define a set of classes with an Id property but the class itself won't know what type of unique identifier is being used until some code instantiates the whole class. Obviously this has a big drawback: if you want to change the unique identifier type, you'll need to change all class instantiations...

Anyway, a massive find & replace using a regexp like (?:User|Employee|Boss|Document)<([A-Za-z0-9-_]+)> or something like this would be enough to change the type of unique identifier for every domain class in your project!).