NDLRGEN005: Factory generic type not implemented by class¶

Diagnostic Info¶

Property	Value
ID	NDLRGEN005
Category	NexusLabs.Needlr.Generators
Severity	Error
Enabled	Yes

Description¶

This error is raised when a class uses [GenerateFactory<T>] with a type parameter T that the class does not implement. The generic type must be an interface or base class that the decorated class implements or inherits from.

Example¶

Code that triggers the error¶

using NexusLabs.Needlr.Generators;

public interface IRequestHandler { }
public interface IMessageHandler { }

// ❌ NDLRGEN005: MyHandler does not implement IMessageHandler
[GenerateFactory<IMessageHandler>]
public class MyHandler : IRequestHandler
{
    public MyHandler(ILogger logger, Guid correlationId) { }
}

How to fix¶

Use an interface that the class actually implements:

// ✅ Correct - MyHandler implements IRequestHandler
[GenerateFactory<IRequestHandler>]
public class MyHandler : IRequestHandler
{
    public MyHandler(ILogger logger, Guid correlationId) { }
}

Or implement the interface you want to use:

// ✅ Correct - MyHandler now implements IMessageHandler
[GenerateFactory<IMessageHandler>]
public class MyHandler : IRequestHandler, IMessageHandler
{
    public MyHandler(ILogger logger, Guid correlationId) { }
}

Or use the non-generic attribute to return the concrete type:

// ✅ Correct - returns concrete MyHandler type
[GenerateFactory]
public class MyHandler : IRequestHandler
{
    public MyHandler(ILogger logger, Guid correlationId) { }
}

Why This Matters¶

The [GenerateFactory<T>] attribute changes the return type of the factory's Create() method from the concrete class to T. If the class doesn't implement T, the generated code would have an invalid cast and fail to compile.

Generated Code Comparison¶

Non-generic [GenerateFactory]:

public interface IMyHandlerFactory
{
    MyHandler Create(Guid correlationId);  // Returns concrete type
}

Generic [GenerateFactory<IRequestHandler>]:

public interface IMyHandlerFactory
{
    IRequestHandler Create(Guid correlationId);  // Returns interface
}