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How to Resolve Error "CS0703: Inconsistent accessibility: constraint type 'type' is less accessible than 'generic'" in C#

The Compiler Error CS0703 is an Accessibility (Visibility) error. The message reads: "Inconsistent accessibility: constraint type 'HiddenType' is less accessible than 'PublicGeneric<T>'".

In C#, you cannot expose a type to the public world if that type depends on something private or internal. Specifically with Generics, if you declare a public generic class Wrapper<T>, you cannot constrain T to inherit from an internal class. If you did, external users would see the Wrapper<T> class but would be unable to use it because they don't have access to the required base class to satisfy the constraint.

This guide explains how to align the visibility levels of your generics and their constraints.

Understanding Accessibility Leaks​

C# enforces strict rules to prevent "leaky abstractions."

  • Public: Visible to everyone (other projects/assemblies).
  • Internal: Visible only within the current project.

If you have: public class Manager<T> where T : Worker

And Worker is internal. An external library tries to use Manager<T>. It sees the class. It reads the constraint: "T must be a Worker". But it cannot see Worker. The external library is now stuck; it has a public tool it cannot use. C# prevents this situation by flagging CS0703.

Scenario 1: Public Class with Internal Constraint​

This is the most common occurrence. You define a helper class or data structure intended to be public, but you restrict it to work only with your internal data models.

Example of error:

// This class is Internal (default)
class InternalModel 
{
    public int Id { get; set; }
}

// ⛔️ Error CS0703: Inconsistent accessibility: 
// constraint type 'InternalModel' is less accessible than 'PublicRepository<T>'.
public class PublicRepository<T> where T : InternalModel
{
    public void Save(T item) { }
}

Solution 1: Reduce Visibility of the Generic Class​

If the generic class (PublicRepository) relies on an internal type (InternalModel), it implies that the repository itself should arguably be internal. External assemblies can't use InternalModel anyway, so they probably shouldn't be using this specific repository.

Solution: change the generic class to internal.

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

// ✅ Correct: Both are internal. No accessibility leak.
internal class InternalRepository<T> where T : InternalModel
{
    public void Save(T item) { }
}

Solution 2: Increase Visibility of the Constraint​

If the generic class must be public (e.g., it is part of a library API), then the type used in the constraint must also be public so that consumers can satisfy the requirement.

Solution: change the constraint type to public.

// ✅ Correct: Now visible to the world
public class PublicModel 
{
    public int Id { get; set; }
}

// ✅ Correct: The constraint is as visible as the generic class.
public class PublicRepository<T> where T : PublicModel
{
    public void Save(T item) { }
}
tip

Interfaces: The same rule applies to interfaces. You cannot have public class Wrapper<T> where T : IInternalInterface. Either the interface becomes public, or the wrapper becomes internal.

Conclusion​

CS0703 ensures your API is usable. You cannot demand that users provide a type they are not allowed to see.

  1. Check Visibility: Look at the class definition (public class X) and the constraint (where T : Y).
  2. Align Them:
    • Make the Generic Class less visible (internal).
    • OR Make the Constraint Type more visible (public).

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