NDLRGEN033: Provider property uses concrete type¶

Diagnostic Info¶

Property	Value
ID	NDLRGEN033
Category	NexusLabs.Needlr.Generators
Severity	Warning
Enabled	Yes

Description¶

This warning is raised when a provider property uses a concrete class type instead of an interface. While this works, using interfaces is generally preferred for better testability and flexibility.

Example¶

Code that triggers the warning¶

using NexusLabs.Needlr.Generators;

public class OrderRepository { }  // Concrete class

[Provider]
public interface IMyProvider
{
    // ⚠️ NDLRGEN033: Consider using an interface
    OrderRepository Repository { get; }
}

How to fix¶

Define an interface for the service:

using NexusLabs.Needlr.Generators;

public interface IOrderRepository { }
public class OrderRepository : IOrderRepository { }

// ✅ Correct: Uses interface type
[Provider]
public interface IMyProvider
{
    IOrderRepository Repository { get; }
}

Why This Matters¶

Using interfaces instead of concrete types:

Testability: Easy to mock in unit tests
Flexibility: Can swap implementations without changing the provider
Dependency Inversion: Follows SOLID principles
Loose Coupling: Reduces dependencies between components

When Concrete Types Are Acceptable¶

This is a warning, not an error. Concrete types are acceptable in some scenarios:

Value objects that have no behavior to mock
Sealed utility classes that are lightweight and deterministic
Third-party classes that don't implement interfaces

To suppress the warning:

#pragma warning disable NDLRGEN033
[Provider]
public interface IMyProvider
{
    ConcreteClass MyProperty { get; }
}
#pragma warning restore NDLRGEN033

Exceptions¶

The warning is not raised for:

Interface types (obviously)
Factory types (ending with "Factory")
Collection types (IEnumerable<T>, etc.)
Other providers (nested provider references)