Inserters should put back items if blocked

[Factoruser]

If the "output" of an inserter is blocked, it should try to put back the items in its hand to the "source". This would also look better, if the inserters go into a "parking position" at train stations.

It would also allow to make multi-use inserters/chests, changing the item filter depending on the destination. Currently, if the destination denies items, the inserter gets deadlocked. It keeps surplus items in its hand, even it its item filter says, these items aren't allowed. Notably also if the source chest has enough space for them.

[Muche]

Lowering an inserter's stack size to 1 will make sure there is always enough empty space at the target to drop its hand, assuming it's the only inserter putting things in.

The suggestion would work for some chests only. It is entirely possible for the source chest to be filled in the meantime and the inserter will end up with an item in hand anyways.
Trying it for belts would pollute them and/or block the inserter as well.
Does not work for assemblers as well.

The end result would be overall inconsistent behaviour of inserters.

[Factoruser]

Erroneous reasoning.

First I'd keep space in the chest, so the inserter wouldn't get blocked. Second, an inserter has a fixed input and output, therefore it can simply "park" regardless, if its input is blocked or not.

[Muche]

So for train unloading, if the station's chest is full, the inserter will try to return the items back to the wagon, right?
And if the train has left in the meantime, you now have inserters parked in the middle of train track, visually the same situation you are trying to change with this suggestion.

Or the "inserter reserving space in the source inventory" would block an empty train with one full outgoing inserter from leaving the station, leading to bugreports of "empty train not respecting the its schedule".

[Factoruser]

Or the "inserter reserving space in the source inventory" would block an empty train with one full outgoing inserter from leaving the station, leading to bugreports of "empty train not respecting the its schedule".

Although beeing somehow incomprehensible: the inserter reserves nothing, it only tries to put back an item if its output is full. I AM reserving space in a chest by using circuits. The parking position of inserters might be a special case in train stations like pumps are different, but it's not important. A train won't be blocked because the putback action will be a single try, it's not a turning of the inserter's direction.

[Muche]

If you're going to use circuits, you can control the inserter's stack size and/or filter, so it only picks up what perfectly fits into target chest.
With wagons it's harder, but depending on desired contents it's doable.

[Factoruser]

If you're going to use circuits, you can control the inserter's stack size and/or filter, so it only picks up what perfectly fits into target chest.
With wagons it's harder, but depending on desired contents it's doable.

Because inserters don't put back what they are holding, this doesn't work. I believe you still will get sometimes a deadlock with stack size 1, and you won't want anyway filling or emptying trains with single-item inserters.

[Muche]

Yes, if you have 12 inserters with stack size 1 inserting the same thing into one wagon that's like one bulk inserter with stack size 12. Of course its hand won't fit, if the item is 2 pieces away from full stack.
That's why it depends on wagon's desired contents. Is it 40 stacks of one item, 40 stacks of 40 different items, or something between?

You just gotta make sure an inserter is able to finish the stack exactly (so stack size 1 helps here) and no other inserter (with the same filter) is active at that time.

[Factoruser]

Why do something easy, if it could be extremely complicated ? Especially with the circuit system of Factorio, that doesn't even have an ELSE in the decider combinator...

[Muche]

Easy mode: dedicate one item per one inserter. Then the state of that inserter "stuck" with items unable to finish inserting is an expected state.

You seem to be trying to insert one item with more inserters, where "stuck" inserter is an nondesired exceptional state, due to increased complexity of uncontrolled race conditions.

[Loren Pechtel]

There are cases where putting it back will fail and leave the inserter holding the item--but that's what we have now. I do agree that putting it back on something that's moving isn't a good idea, but if the source is fixed I see no harm in the inserter making the attempt.

Related, if I change the recipe of a factory please give me anything the inserters were trying to insert as well as whatever was in the factory. Otherwise you're very likely to get a stuck inserter.

[Factoruser]

That assemblers should store ingredients when changing the recipe, use them later if requested, and still continue working is a different suggestion, which would make things also better. But you can use inserters to empty the storage. Annoying is that also items can block the assembler, that are ingredients of the new recipe...

The suggestion with the inserters has a much wider use case. You can make smart assemblers with demand-based production and smart loading stations to load more than 12 different items or different items with higher loading rate.