Fix README allocation claims: V3.1 rename + IValueSender alloc-free correction

[Copilot]

The README incorrectly labeled the new ValueTask features as "V4" (non-breaking, so V3.1) and contained a stale note claiming IValueSender.Send still had boxing overhead — the opposite of what the Unsafe.As change achieved.

Changes

• Version label: What's New in V4 → What's New in V3.1 throughout (ToC, heading, body)
• Allocation table: IValueSender.Send row updated from "Reduced allocation" → "Zero allocation — fully alloc-free in the mediator infrastructure"
• Note: Rewrites the allocation explanation to be accurate:
  • IValueSender.Send + IValueRequestHandler (no behaviors): fully alloc-free — Unsafe.As reinterpret, struct ValueTask<TResponse> return, non-async generated Handle_Xxx method, nothing heap-allocates
  • IValuePublisher.Publish: same zero-cost dictionary routing, but the generated notification fan-out uses async iteration, which may allocate when handlers are genuinely asynchronous — "dispatch layer" qualifier retained for this row

Path	Before	After
IValueSender.Send + IValueRequestHandler	Reduced allocation / "still has boxing overhead"	Zero allocation — fully alloc-free
IValuePublisher.Publish + IValueNotificationHandler	Zero allocation in dispatch layer	Zero allocation in dispatch layer (unchanged, accurate)

Original prompt

In the CodeGenerator.cs file, specifically within the Send and IValueSender.Send method implementations, replace the standard casts with Unsafe.As to avoid redundant type checks and boxing for ValueTask return types.

Currently, the generated mediator has dictionary lookup as follows:

if (TaskSendSwitchCase.Cases.TryGetValue(request.GetType(), out var handle))
{
    return (global::System.Threading.Tasks.Task<TResponse>)handle(this, request, cancellationToken);
}

And for ValueTask:

if (ValueSendSwitchCase.Cases.TryGetValue(request.GetType(), out var handle))
{
    return (global::System.Threading.Tasks.ValueTask<TResponse>)handle(this, request, cancellationToken);
}

The dictionary value type is Func<{{className}}, object, CancellationToken, object>.

This causes boxing for any value type (like ValueTask<TResponse>).

The goal is to:

1. Change the dictionary value types for TaskSendSwitchCase and ValueSendSwitchCase to object.
2. Update the GenerateTaskSendCase and GenerateValueSendCase methods to remove the (object) cast within the generated delegates.
3. In the Send<TResponse> and IValueSender.Send<TResponse> implementations, use Unsafe.As to cast the object delegate to the specialized Func signature and then call it.

Example for ValueTask:

if (ValueSendSwitchCase.Cases.TryGetValue(request.GetType(), out var handle))
{
    return global::System.Runtime.CompilerServices.Unsafe.As<object, global::System.Func<{{className}}, global::Mediator.Switch.IRequest<TResponse>, global::System.Threading.CancellationToken, global::System.Threading.Tasks.ValueTask<TResponse>>>(handle)(this, request, cancellationToken);
}

This ensures that the returned ValueTask<TResponse> is never cast to object, thus avoiding boxing entirely.

Files to modify:

• src/Mediator.Switch.SourceGenerator/Generator/CodeGenerator.cs

Base branch for PR: copilot/implement-hybrid-valuetask-support

This pull request was created from Copilot chat.

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.