OpenDecoratorForAttribute

NexusLabs.Needlr.Generators ¶

OpenDecoratorForAttribute Class¶

Marks a generic class as a decorator for all closed implementations of an open generic interface. This is a source-generation only feature - the generator discovers all closed implementations at compile time and emits decorator registrations for each.

public sealed class OpenDecoratorForAttribute : System.Attribute

Inheritance System.Object 🡒 System.Attribute 🡒 OpenDecoratorForAttribute

Example¶

public interface IHandler<T>
{
    Task HandleAsync(T message);
}

// Concrete handlers
public class OrderHandler : IHandler<Order> { ... }
public class PaymentHandler : IHandler<Payment> { ... }

// Open generic decorator - applies to ALL IHandler<T> implementations
[OpenDecoratorFor(typeof(IHandler<>))]
public class LoggingDecorator<T> : IHandler<T>
{
    private readonly IHandler<T> _inner;
    private readonly ILogger<LoggingDecorator<T>> _logger;

    public LoggingDecorator(IHandler<T> inner, ILogger<LoggingDecorator<T>> logger)
    {
        _inner = inner;
        _logger = logger;
    }

    public async Task HandleAsync(T message)
    {
        _logger.LogInformation("Handling {Type}", typeof(T).Name);
        await _inner.HandleAsync(message);
        _logger.LogInformation("Handled {Type}", typeof(T).Name);
    }
}

// Generator emits:
// services.AddDecorator<IHandler<Order>, LoggingDecorator<Order>>();
// services.AddDecorator<IHandler<Payment>, LoggingDecorator<Payment>>();

Remarks¶

Use this attribute when you want to apply a single decorator implementation to ALL closed types of an open generic interface. For example, to add logging to every IHandler<T> implementation.

The decorated class must: - Be an open generic class with matching type parameter arity - Implement the open generic interface specified - Accept the open generic interface as a constructor parameter (to wrap the inner service)

At compile time, the source generator: 1. Discovers all closed implementations of the open generic interface 2. Emits AddDecorator<TService, TDecorator> for each closed type

Constructors¶