Allow on_pre events to return false and abort the event

[sparr]

I would like to be able to return false (or some other sentinel value) from my event handler for on_pre_* events and cause the rest of the event to not happen. This would work like browser javascript event handlers that disable the default functionality for the event that is being triggered.

[Ranakastrasz]

On that thought, I would like to be able to have you change any of the arguments the event handler holds, and have it use those instead.

[Rseding91]

Factorio events don't support this concept. In fact the game itself doesn't support this concept.

So, this isn't likely to ever happen.

[SilverB1rd]

When trying to build a new entity in a location that is not valid, like a furnace on top of belts, the game stops the player from building the object. I don't know if this concept really applies to on_pre or on_put_item events. However something like on_validate_entity_placement event where placement could be denied before the game starts the on_put_item -> on_built_entity event chain would be very useful for scenarios I'm currently working on.

I work around this right now by deleting the entity in on_built_entity and refunding the item to the player's inventory, which is not really intuitive.

[mickael9]

In case you didn't know, you can cancel an item placement by doing player.clean_cursor() in on_put_item (before on_built_entity gets raised). Of course the player won't have the item in hand anymore after this. Similarly, you can change what is being placed by changing the player's cursor_stack in on_put_item.

[doc]

In case you didn't know, you can cancel an item placement by doing player.clean_cursor() in on_put_item (before on_built_entity gets raised). Of course the player won't have the item in hand anymore after this. Similarly, you can change what is being placed by changing the player's cursor_stack in on_put_item.

What happens if the player has no inventory space available?

[Mooncat]

In case you didn't know, you can cancel an item placement by doing player.clean_cursor() in on_put_item (before on_built_entity gets raised). Of course the player won't have the item in hand anymore after this. Similarly, you can change what is being placed by changing the player's cursor_stack in on_put_item.

What happens if the player has no inventory space available?

Either drop the item on ground or put it back to the cursor in the next tick and hopefully no one will notice?

[darkfrei]

Either drop the item on ground or put it back to the cursor in the next tick and hopefully no one will notice?

You can place and remove on the same tick, but you can get dust of placing.