Middleware to deep-freeze all state

[LPGhatguy]

It'd be cool to have a middleware that automatically makes all items in the store read-only. It'd be similar to the JS package 'deep-freeze', but probably throw errors on mutations instead of silently ignoring them.

Speed of implementation doesn't really matter here, since it'd only be a development tool.

Implementing this in Lua 5.1 might be tricky. Normally for a read-only table, I'd create a new table with __index and __newindex metamethods acting as a proxy, but then you wouldn't be able to iterate (or shallow copy) the table! In 5.2, Lua gained __pairs and __ipairs which would've helped here, but alas.

There might be one edge case in this implementation. Way back when I first used Redux, I would keep JS Promise objects in the store as a way to manage request status. Promise objects have internal mutability, which we might consider to be breaking the Redux paradigm, but because it's not observable outside of attaching a handler to the promise, I don't know if it is. If we wanted to support a use case like that, we'd need to make sure not to deep-freeze some objects, or force Promise objects to be userdata instead.

[LPGhatguy]

I don't think we need to support Promise objects in the store.

I haven't gained any insight into how to actually deep-freeze tables. 😦

[AmaranthineCodices]

I'm not sure if deep-freezing tables is even possible in Lua without __pairs and __ipairs. Deep-freezing in Lua 5.1 must either:

• Allow mutations of existing keys (bad)
• Not allow iteration over the frozen table (also bad)

[Kampfkarren]

table.freeze is now out, so this is doable.

I don't think we need to support Promise objects in the store.

In my own systems, I check getmetatable(table) ~= nil as a heuristic for whether or not to freeze or not. Not sure how good it is as a generality.