Privatest

Privatest is a code analyzer that adds instance-level accessibility mode to C#.

Setup

To set it up simply install the Privatest Nuget package in your project:

dotnet add package Privatest

Usage

To assign an instance-level accessibility mode to a member of a class, decorate it with the [This] attribute.

public class Class
{
   [This] private int _field;

   public void Method(Class other)
   {
      _field = 10; // OK

      other._field = 10; // ERROR
    //^^^^^^^^^^^^ `_field` is inaccessible due to its protection level. It can only be accessed by the instance to which it belongs (through the `this` reference).
   }
}

You can apply the [This] attribute on fields, methods and properties (including property getters and setters).

The [This] attribute can only be applied on private members.

public class Class
{
   [This] public int Property { get; set; }
                   //^^^^^^^^ [This] attribute can be applied only on private members, but was applied on 'Public' member 'Property'
}

The [This] attribute can also be used to limit the accessibility of a member to a specific scope only. It can be useful when working with backing fields, which should be accessed only by the associated properties.

public class Class
{
   [This(nameof(FrontProperty))] private int _backField;
   public int FrontProperty
   {
      get => _backField;
      set => _backField = value;
   }

   public void Method(Class other)
   {
      _backField = 2;
    //^^^^^^^^^^ `_backField` is inaccessible due to its protection level. It can only be accessed in `FrontProperty` (but is used in `Method`).
   }
}

The scope can be limited to any method or property of a class. It can by specified either by using the nameof operator or as a plain string value.

In case of backing fields that have the same name as their front properties (just starting with a lower case letter and/or _ character), one can also use the [BackingField] attribute which will work the same way as a longer [This(nameof(FrontPropertyName))].

public class Class
{
   [BackingField] private int _name;
   public int Name
   {
      get => _name;
      set => _name = value;
   }
   
   public int Surname
   {
      get => _name;
           //^^^^^ `_name` is inaccessible due to its protection level. It can only be accessed in `Name` (but is used in `Surname`).
   }
}

How does it work?

Privatest is a C# code analyzer that performs accessibility checks during the compilation stage only (using Roslyn hooks). It does not introduce any additional checks in the compiled code and therefore does not impact its performance.

Contributions

I am open to PRs as well as github issues.