undefined | Better HN

0 pointsmajormajor1y ago0 comments

I don't follow the connection you're making.

State machines often are implemented with mutable objects.

And one does not need mutable objects to make "modules-> objects with the transitions being method calls". Every method call could return a fresh, immutable object, nothing requires mutation there.

I'd see a method like:

`TransitionTo(newState)`

as a major smell compared to an explicit

`TransistionToNewState`

and I think OOO can be helpful (hardly required, of course) in that one neat way of streamlining usage of your code is that if you're implementing objects then the object for something in "State A" might not even have "TransitionToStateC" if that's not a valid operation.

(No, you don't HAVE to write state machine code that allows you to ask for invalid operations, but it's a common pattern I've seen in real code and in online discussion/blogs/stack overflow.)

0 comments

grumpyprole1y ago

Objects and "method calls" generally implies mutable state to me, but yes the parent was not explicit about this. I assumed mutable (implicit) state was being argued in favour of an explicit state representation. Perhaps I misunderstood.

For a state machine, I would expect a function such as:

transition : (old_state, event) -> new_state

Or if we use immutable objects, and one method per simple event, then something like:

transition_event1 : () -> new_state

Which I think is similar to what you hace. So I think we are in agreement here.

saurik1y ago

> I assumed mutable (implicit) state was being argued in favour of an explicit state representation.

I definitely was not: I would argue for structured logic rather than implicit state. The idea you are discussing seems to be more about imperative vs. functional design, and that would also be a lot better... but these are Google engineers managing a million interacting state machines via a giant pile of global (mutable) state, resulting in tons of bugs such as this one that isn't even fixed yet:

https://issues.webrtc.org/issues/339131894

A reply I just left elsewhere on this thread, noting that "state machine" doesn't imply the clean perfectly-factored concept you'd learn in a computer science class: these are ad hoc state machines that result from having a number of developers who don't really care and who think they can "dead reckon" the state of the system if they just add enough transition functions.

https://news.ycombinator.com/item?id=42250142

grumpyprole1y ago

> these are Google engineers managing a million interacting state machines via a giant pile of global (mutable) state

Yeah that doesn't sound good. I understand the point you are making now and agree.

InDubioProRubio1y ago

The problem is, that the state transition information is usually a complex set of events unleashed upon the little world build into objects. Its basically a small reality simulation, parametrized by all sides, similar to a physics simulation with the external world filtered being input.

Now, if we said to someone to model a weather prediction via state-machine- that would be obvious madness. But if we take a small object (like a cubic meter of air) and modelled that part to handle inputs and transfer forces, that generic statemachine will do the job- because the atmospheric ocean of statemachines knows more about the whole system, than a single statemachine.

My point is- there is state in a system, that is not explicitly modeled.

j / k navigate · click thread line to collapse

0 pointsmajormajor1y ago0 comments

I don't follow the connection you're making.

State machines often are implemented with mutable objects.

And one does not need mutable objects to make "modules-> objects with the transitions being method calls". Every method call could return a fresh, immutable object, nothing requires mutation there.

I'd see a method like:

`TransitionTo(newState)`

as a major smell compared to an explicit

`TransistionToNewState`

(No, you don't HAVE to write state machine code that allows you to ask for invalid operations, but it's a common pattern I've seen in real code and in online discussion/blogs/stack overflow.)

0 comments

grumpyprole1y ago

For a state machine, I would expect a function such as:

transition : (old_state, event) -> new_state

Or if we use immutable objects, and one method per simple event, then something like:

transition_event1 : () -> new_state

Which I think is similar to what you hace. So I think we are in agreement here.

saurik1y ago

> I assumed mutable (implicit) state was being argued in favour of an explicit state representation.

https://issues.webrtc.org/issues/339131894

https://news.ycombinator.com/item?id=42250142

grumpyprole1y ago

> these are Google engineers managing a million interacting state machines via a giant pile of global (mutable) state

Yeah that doesn't sound good. I understand the point you are making now and agree.

InDubioProRubio1y ago

My point is- there is state in a system, that is not explicitly modeled.

j / k navigate · click thread line to collapse