Lua Version Compatibility

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This page is dedicated to information on ensuring that Lua code remains compatible across multiple versions of Lua (e.g. 5.1 and LuaFiveTwo), as well as different LuaImplementations.

The Lua Reference Manual lists "Incompatibilities with the Previous Version" [5.1] [5.2-alpha]. The Lua 5.2.0-alpha documentation lists [Changes since 5.1] (see also LuaFiveTwo).
Bytecode: Lua 5.1 and Lua 5.2.0-alpha are not bytecode compatible, and LuaJit 2.x doesn't support the standard Lua interpreter's bytecodes. Even within a single version of Lua (5.1), bytecode on different platforms (e.g. Intel x86, Intel x86-64, and PPC) may not be compatible. Source code is more compatible, and source code can be minified (e.g. see squish: CompressionAndArchiving). This typically affects C modules that bundle compiled bytecode (e.g. via BinToCee) and has affected MetaLua.
Source lexing: Lua 5.1 and 5.2.0-alpha use the same tokens, although there are some lexical differences involving things like locales [1] and perhaps [4].
[Lua Compat-5.1] provides an implementation of the Lua 5.1 package model to be used with Lua 5.0.
CompatibilityWithLuaFive shows how to make your code compatible with all Lua 5.X versions.
Bit libraries: LuaFiveTwo (5.2.0-alpha) and LuaJit (Lua BitOp) come with different built-in bit libraries, which are compatible to only some extent (e.g. signedness/overflow). Lua BitOp can be installed on 5.2, and see also [bit32 for Lua 5.1?]. [lua-bit-numberlua] provides a bit library with Lua 5.2 "bit32" and LuaBitOp "bit" compatibility interfaces.
[lua-compat-env] provides Lua 5.1/5.2 environment compatibility functions: load, loadfile, getfenv, and setfenv for use in 5.1 and 5.2
[lua-parser-loose] provides an implementation of _ENV in Lua 5.1.
Version check. The global Lua variable _VERSION contains the Lua version string (e.g. "Lua 5.1" [2] or "Lua 5.2" [3]. (Note: LuaJit 2.0-beta reports the Lua version as 5.1.) LuaFiveTwo contains new library functions: [lua_version] and [luaL_checkversion]. In C code, lua.h of Lua 5.1 contains these defines:

#define LUA_VERSION	"Lua 5.1"
#define LUA_RELEASE	"Lua 5.1.4"
#define LUA_VERSION_NUM	501

: There are reasons to prefer capability detection over version detection [5]. Doing tests like _VERSION == "Lua 5.2" will almost certainly break in 5.3. _VERSION ~= "Lua 5.1" will more likely be forward compatible, though will break in 5.0 (if that matters).

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Last edited March 1, 2014 6:44 pm GMT (diff)