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RequestHandlerDelegate

Namespace: RA.Utilities.Dispatcher.Models

The RequestHandlerDelegate delegates are what IPipelineBehavior receives as its next parameter — invoking them runs the next stage of the request pipeline.

📦 Type Definition​

/// <summary>Represents a delegate for handling a request without a response.</summary>
public delegate ValueTask<Result> RequestHandlerDelegate();

/// <summary>Represents a delegate for handling a request with a response.</summary>
public delegate ValueTask<Result<TResponse>> RequestHandlerDelegate<TResponse>();

/// <summary>Context-aware variant for a request without a response.</summary>
public delegate ValueTask<Result> RequestHandlerContextDelegate<TContext>(PipelineContext<TContext> context)
    where TContext : class, new();

/// <summary>Context-aware variant for a request with a response.</summary>
public delegate ValueTask<Result<TResponse>> RequestHandlerContextDelegate<TResponse, TContext>(PipelineContext<TContext> context)
    where TContext : class, new();

🎯 Purpose​

The dispatcher composes pipeline behaviors around the handler into a delegate chain. Each behavior's HandleAsync receives a delegate that invokes the next behavior — or the handler itself, innermost. The delegate returns ValueTask<Result<TResponse>> (ValueTask<Result> for void requests): the handler's result on success, or Result.Failure(...) on expected failure.

Behavior InterfaceDelegate Parameter TypeReturn Type
IPipelineBehavior<TRequest>RequestHandlerDelegateValueTask<Result>
IPipelineBehavior<TRequest, TResponse>RequestHandlerDelegate<TResponse>ValueTask<Result<TResponse>>

The context-aware variants are used by the HandleAsync<TContext> overloads; the default interface implementations adapt the plain delegate by closing over the context (() => next(context)).

🚀 Usage​

public class TimingBehavior<TRequest, TResponse> : IPipelineBehavior<TRequest, TResponse>
    where TRequest : IRequest<TResponse>
{
    public async ValueTask<Result<TResponse>> HandleAsync(
        TRequest request, RequestHandlerDelegate<TResponse> next, CancellationToken cancellationToken)
    {
        var stopwatch = Stopwatch.StartNew();
        Result<TResponse> result = await next(); // runs the inner pipeline (or the handler)
        Console.WriteLine($"Handled in {stopwatch.ElapsedMilliseconds} ms");
        return result;
    }
}

🧠 Notes​

  • No delegate chain without behaviors — when a request has no pipeline behaviors, the generated mediator invokes the handler directly and no delegate is allocated at all.
  • The delegate is what lets a behavior short-circuit: return a failed Result without calling next().

🔗 Related​