Slot

A named place on an entity that another part fills: a wheel mount, an engine bay, a seat, a weapon hardpoint, a socket in a modular wall, a mount on a ship. The entity carrying Slot is where the part attaches: the part is built as a child of that entity and stands at its transform. Put a Slot on an empty child positioned where the part goes, one per slot.

What fills the slot is held by the Assembly on the slot's root (the nearest Assembly on the entity or above it; one on a part built into a slot passes the slot on to the Assembly holding that part), by the slot's path. A slot under no Assembly holds its default.

Fields

Field	Type	Notes
name	string	The name the slot answers to in paths; empty takes the entity's name.
kind	string	The kind of part it takes (wheel, engine, seat). A part fits when its Part.fits names this kind. Empty takes any part.
tags	{ string }	Asset tags a part must carry, all of them, to fit.
default	instantiable asset	The part filling the slot when its Assembly names none.
joint	table	Joint fields binding the part's body to the body the slot stands on ({ kind = "hinge", axis = { 1, 0, 0 } }); the Joint component on the part's root is added with connected set to the slot. Empty seats the part as a child alone.

Paths

A slot's path is its name, under the path of the slot whose part it stands in: an engine part carrying a turbo slot, filled into the engine slot, puts that slot at engine/turbo. Paths are what Assembly:fill, Assembly:resolve and the saved configuration use.

Methods

Method	Returns	Notes
:path()	string	This slot's path in its Assembly.
:assembly()	Assembly or nil	The Assembly that holds it.
:fill(part)	entity or nil	Fill through the Assembly (Assembly:fill(self:path(), part)); raises when the part does not fit, naming why.
:empty()		Leave it empty, its default included.
:fits(part)	(boolean, string)	Whether a part fits, and why or why not.
:filled()	{ part, entity, source } or nil	The part filling it and the entity it was built on.
:refresh()	entity or nil	Rebuild the part when it differs from what the Assembly names.

Usage

-- A body with a wheel slot and an engine slot
local body = entity.spawn("buggy")
body.component.add("Assembly")
local fl = entity.spawn("wheel_fl", { parent = body.id, position = { x = -0.8, y = 0.3, z = 1.2 } })
fl.component.add("Slot", { kind = "wheel", default = "parts.StockWheel" })
local bay = entity.spawn("engine", { parent = body.id, position = { x = 0, y = 0.5, z = 1 } })
bay.component.add("Slot", { kind = "engine" })

bay.component.get("Slot"):fill("parts.V8")
print(fl.component.get("Slot"):fits("parts.V8"))  -- false, "slot 'wheel_fl' takes parts of kind 'wheel'; 'parts.V8' fits { engine }"

Put the same children in a bundle (asset.create("bundle", "Buggy", { entity = body })) and every instance of the bundle carries the slots. The Assembly README covers configurations, the resolver, undo, multiplayer and saving.