Immutable data structures are constant, unmodifiable data structures that can simply be only read. You can instantiate them only once and through the whole program this data will remain unchanged until you delete them. This opens up powerful abilities when used wisely in e.g. Data Oriented, Reactive, Distributed, Event-based, Flow-based or Functional programming, etc.
Lua does not offer immutable tables as a language feature, but it can be simulated to a fairly good degree in runtime. I think I stretched it enough to publish a module I use for making immutable tables in Lua.
I present to you “IMMUTABLE”:
IMMUTABLE makes any Lua table runtime immutable (read-only) where one:
- can get defined entries
- cannot add, remove nor change entries
- cannot access values at undefined keys nor out of bounds elements
Usage:
Step 1. Require it:
local IMMUTABLE = require "immutable.immutable"
Step 2. Create an immutable table (3 ways):
local data_table = { 1, 2, 3 } -- regular table
-- convert any table to an immutable table:
--[[1]] local my_immutable_table = IMMUTABLE.make( data_table )
-- or simply using convenience call:
--[[2]] local my_immutable_table = IMMUTABLE( data_table )
-- or create it on the go (syntax sugar for call with table parameter):
--[[3]] local my_immutable_table = IMMUTABLE{ 1, 2, 3 }
API:
IMMUTABLE.make(original_table)
-- Function to make a table immutable, including nested tables
@param original_table [table] - table to convert to immutable table
@return [table] - original table converted to immutable table
IMMUTABLE.is_immutable(table_to_check)
-- Function to check if a given table `t` is immutable
@param table_to_check [table] - table to check
@return [bool] - true if table t is immutable, false otherwise
Known issues:
-
Keys referencing
nilin the original table will be inaccesible in the immutable table.
To prevent unidentified key access, initialize the fields with any other value. -
Immutable tables are secured against modifications in any sort of loops, but are not secured against usage with
tableAPI (because table API functions ommit __index calls)table.insert(immutable{ 1, 2 }, 3, 3) -- will NOT raise an error! table.remove(immutable{ 1, 2 }, 2) -- will NOT raise an error!Known workaround is to override the table API functions, for example insert and remove. Example of this is provided in README.
License: MIT
Source code:
Above is a general use Lua module for everyone coding in Lua. If you wish to add IMMUTABLE as Defold dependency, use link from the below repository instead
An example of a Tic Tac Toe game I created in Defold using it:
I am interested myself even, how does they solve it in Lua translation