CHR0004: Reactor method signature must match allowed signatures

Rule Description

Methods in reactor classes must follow one of the allowed signatures for event handling. This ensures proper integration with Chronicle’s reactor infrastructure.

Severity

Warning

Allowed Signatures

Event handler methods in reactors must have one of the following signatures:

// Async with event only
Task MethodName(TEvent @event)

// Async with event and context
Task MethodName(TEvent @event, EventContext context)

// Synchronous with event only
void MethodName(TEvent @event)

// Synchronous with event and context
void MethodName(TEvent @event, EventContext context)

Where TEvent is a type marked with [EventType].

Example

Violation

public class OrderReactor : IReactor
{
    // CHR0004: Invalid signature - returns Task<bool> instead of Task
    public async Task<bool> OrderCreated(OrderCreated @event)
    {
        // Process event
        return true;
    }

    // CHR0004: Invalid signature - third parameter not allowed
    public async Task OrderUpdated(OrderUpdated @event, EventContext context, string extraParam)
    {
        // Process event
    }
}

Fix

public class OrderReactor : IReactor
{
    // Valid signature
    public async Task OrderCreated(OrderCreated @event)
    {
        // Process event
    }

    // Valid signature with context
    public async Task OrderUpdated(OrderUpdated @event, EventContext context)
    {
        // Process event
    }

    // Valid synchronous signature
    public void OrderShipped(OrderShipped @event)
    {
        // Process event
    }
}

Why This Rule Exists

Reactors are a core pattern in Chronicle for handling side effects when events occur. Standardized method signatures ensure:

• Predictable reactor behavior
• Proper infrastructure integration
• Clear code patterns across the codebase
• Reliable event handling

Related Rules

• CHR0005: Reactor event parameter must have [EventType] attribute
• CHR0006: Reducer method signatures