Factorio Forums

The output of serpent.block may change if a table in the global table is copied using table.deepcopy

Steps to reproduce:
- create a table that may change with - save the game, exit to main menu and load the game again
- observe that the output /c game.print(serpent.block(global.t)) and /c game.print(serpent.block(table.deepcopy(global.t))) differs

Thanks for the report however this isn't a bug. A copy of a table is not the same as the original table.

Actually, I think this is a bug. And it's trivial to desync the game without having to involve any copying of the table.

Steps to reproduce:
- Run the command in my previous post that creates global.t in a multiplayer server with nobody in
- Connect to the server
- Run /c game.print(serpent.block(global.t))
- The client desyncs

Should probably just change this bug report title to "sparse arrays are improperly serialized", the result of #global.t.item_counts differ between the server and the client after the setup descried in my previous post.

This looks like another case of Lua treating initializer-list construction differently from table = {}, table[...] = ...

I'll look into it and see what I can find. Although i wonder what the use-case is for making a sparse-table through initializer list syntax instead of per-element syntax.

The 5.2 reference manual says the result of #table is undefined if the table is sparse, the 5.3 reference says it may return any value which is the index of an element where the next index is nil. Serpent uses #table when determining to make it sparse or not, but after a table in global has been saved and loaded it's length may be reported differently causing serpent to output different results.