[Plugins] Any way to store objects in the plugin state, i.e. for OOP?

[drewlwhitney]

Describe the question

I've read the Sendables section of the plugin docs.

I'm making a plugin that would benefit from OOP. I'm tracking when files are deleted, renamed, or moved, and allowing those operations to be undone. It would be great to store an object with a .undo() method, so I don't have to check what kind of undo operation it is. Is there any way to store such an object in the state you get from ya.sync(), or do I need to add a kind tag to the object instead of a method?

So far it seems like storing any object that has functions (other than Url) causes an error.

Thanks!

Checklist

• I have read all the documentation
• I have searched the existing discussions/issues

[pballada]

Functions can't go into the state from your async code. Everything you pass into or return from a ya.sync() block crosses threads, and only sendable values can make that trip: nil, booleans, numbers, strings, Url, and tables of those. A method is a function, so it gets rejected, and a metatable isn't carried across either.

You can still have op:undo(), though. Keep the data sendable and the behavior in your plugin. Store a plain record with a kind, then attach the methods with a metatable after you read it back:

-- Behavior lives at module level and never crosses threads.
local Op = {}
Op.__index = Op

local undo_by_kind = {
	rename = function(op) --[[ move op.to back to op.from ]] end,
	move   = function(op) --[[ move op.to back to op.from ]] end,
	delete = function(op) --[[ restore op.path from the trash ]] end,
}

function Op:undo() return undo_by_kind[self.kind](self) end

local function as_op(record) return record and setmetatable(record, Op) end

-- State only holds plain, sendable records (store paths as strings).
local push = ya.sync(function(state, record)
	state.history = state.history or {}
	table.insert(state.history, record)
end)

local pop = ya.sync(function(state)
	return state.history and table.remove(state.history)
end)

return {
	entry = function()
		-- recording: push { kind = "rename", from = "/a/old.txt", to = "/a/new.txt" }
		local op = as_op(pop())
		if op then
			op:undo()
		end
	end,
}

The kind tag is still there, but only as_op and the undo_by_kind table ever look at it. Adding a new operation means adding one entry to that table. The rest of your code just calls op:undo().

If you'd rather have one class per kind, map the kind to the class instead: setmetatable(record, classes[record.kind]).

[drewlwhitney]

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