[mrkeen]

> now with events that are harder to trace than function calls would have been

I don't know how this could be true. Events are things - nouns which can be backed-up, replicated, stored, queried, rendered, indexed and searched over.

[sattoshi]

How is it not true? Instead of tracking data and function calls over a unified stacktrace, you track Things and Messages over databases, queues, and logs —- none of which you can trivially attach a debugger to.

I generally like event-driven architecture, but I need to admit that debuggability is sacrificed where it matters most.

[lmm]

There's no "find usages" for events, and it becomes harder to find out why something didn't happen. A function call can't simply "not return" - in the worst case you get an exception, or a stuck thread in the caller that will show up in a stack dump. But downstream event processing can very easily just not happen, for one of many different reasons, and out-of-the-box it's often difficult to investigate.

[friendzis]

> A function call can't simply "not return"

Remember "callback hell"? Assumption that a function call returns after running to completion requires rather specific synchronous cascading architecture, which WILL break in multithreaded code. Most of the multithreaded function calls will set a flag in shared memory and return early, expecting caller to poll.

If your API is based on single entry-point `invokeMethod(callee, method)` it is equally untraceable to event entry point `fireEvent(producer, event)`.

[lmm]

> Most of the multithreaded function calls will set a flag in shared memory and return early, expecting caller to poll.

Which is exactly switching from function calls to event-driven architecture, and the problems with that are exactly the problems we're talking about.

[friendzis]

The problems you describe are inherent to indirect invocations and are related to event-driven architectures only because typical event dispatching architecture is built on non-blocking calls.

You do not even need return-early (non-blocking) semantics for these problems to manifest. You can implement a giant string-keyed vtable for all methods in your program (or use a language with advanced reflection capabilities) and will have exactly the same problems. Namely there probably won't be tooling to match caller-callee pairs, which is the core issue here.

[soulofmischief]

In JavaScript,

  const
    myEvent = 'myEvent', 
    target = new EventTarget()

  target.on( myEvent, () => {
    console.log( "It's easy to introspect well-organized code." )
  })

  target.dispatchEvent( new Event( myEvent ))

[lmm]

Yeah, good luck remembering to do that up-front for every event handler. You missed one? Whoops, enjoy the information you wanted silently not being there when you need it.

[soulofmischief]

Remembering to do what? Properly maintain a list of constants and enums to use throughout my application?

That's not something I have to remember or forget, it's a simple habit that is as natural as importing and referencing a function.

As a general rule, numbers and string literals should never be hardcoded. Internalizing this should be a base expectation of any high-performing team member.