Lua Five Features

wiki

Changes from version 4.0 to 5.0

(from HISTORY file in distribution)

Language

• lexical scoping.
• Lua coroutines.
• standard libraries now packaged in tables.
• tags replaced by metatables and tag methods replaced by metamethods, stored in metatables.
• proper tail calls.
• each function can have its own global table, which can be shared.
• new __newindex metamethod, called when we insert a new key into a table.
• new block comments: --[[ ... ]].
• new generic for.
• new weak tables.
• new boolean type.
• new syntax "local function".
• (f()) returns the first value returned by f.
• {f()} fills a table with all values returned by f.
• \n ignored in [[\n .
• fixed and-or priorities.
• more general syntax for function definition (e.g. function a.x.y:f()...end).
• more general syntax for function calls (e.g. (print or write)(9)).
• new functions (time/date, tmpfile, unpack, require, load*, etc.).

API

• chunks are loaded by using lua_load; new luaL_loadfile and luaL_loadbuffer.
• introduced lightweight userdata, a simple "void*" without a metatable.
• new error handling protocol: the core no longer prints error messages; all errors are reported to the caller on the stack.
• new lua_atpanic for host cleanup.
• new, signal-safe, hook scheme.

Implementation

• new license: MIT.
• new, faster, register-based virtual machine.
• support for external multithreading and coroutines.
• new and consistent error message format.
• the core no longer needs "stdio.h" for anything (except for a single use of sprintf to convert numbers to strings).
• lua.c now runs the environment variable LUA_INIT, if present. It can be "@filename", to run a file, or the chunk itself.
• support for user extensions in lua.c. Sample implementation given for command line editing.
• new dynamic loading library, active by default on several platforms.
• safe garbage-collector metamethods.
• precompiled bytecodes checked for integrity (secure binary dostring).
• strings are fully aligned.
• position capture in string.find.
• read('*l') can read lines with embedded zeros.