src/on_gc.luau

@@ -0,0 +1,40 @@
+if not game then script = require "test/relative-string" end
+
+local flags = require(script.Parent.flags)
+local throw = require(script.Parent.throw)
+
+
+-- array of all cleanup callbacks
+local cleanup_callbacks = {} :: { [number]: () -> () } -- always dense
+-- weak array of all cleanup lifetimes
+local cleanup_lifetime = {} :: { [number]: unknown } -- can be sparse
+setmetatable(cleanup_lifetime :: any, { __mode = "v" })
+
+local function on_gc(lifetime: unknown, callback: () -> ())
+    local id = #cleanup_callbacks + 1
+    cleanup_lifetime[id :: any] = lifetime -- todo
+    cleanup_callbacks[id] = callback
+end
+
+local function sweep()
+    for id = #cleanup_callbacks, 1, -1 do
+        if cleanup_lifetime[id] == nil then -- lifetime was garbage collected
+            local callback = cleanup_callbacks[id]
+
+            do -- swap and pop
+                local max_id = #cleanup_callbacks
+
+                cleanup_callbacks[id] = cleanup_callbacks[max_id]
+                cleanup_callbacks[max_id] = nil
+
+                cleanup_lifetime[id] = cleanup_lifetime[max_id]
+                cleanup_lifetime[max_id] = nil
+            end
+
+            local ok, err: string? = pcall(callback)
+            if not ok then warn(`error occured during cleanup: {err}`) end
+        end
+    end
+end
+
+return function() return on_gc, sweep end