Dump of Lua code snippets

lua-dump.md

Lua Dump

This is a dump of random Lua code snippets. Use them however you like.

License

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.

In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to http://unlicense.org/

atexit.lua

--- Call cleanup functions when the program terminates

local handlers = {}

local function cleanup()
  for i, v in ipairs(handlers) do
    pcall(v)
  end
  handlers = {}
end

-- ew
_G.__atexitgc__ = newproxy(true)
getmetatable(_G.__atexitgc__).__gc = cleanup

local oldexit = os.exit
function os.exit(...)
  cleanup()
  return oldexit(...)
end

--- Register a function to be called when the program terminates
function atexit(f)
  table.insert(handlers, f)
end

return atexit

rawtostring.lua

--- Return the default tostring representation of a table even if its metatable
--- redefined __tostring. __metatable breaks this though.
function rawtostring(o)
  local mt = getmetatable(o)
  local s
  if mt and mt.__tostring then
    local oldtostring = mt.__tostring
    mt.__tostring = nil
    s = tostring(o)
    mt.__tostring = oldtostring
  else
    s = tostring(o)
  end
  return s
end

strict.lua

--- Set a metatable that disallows getting undefined/nil and setting any members
--- on a table.
--- Can be disabled temporarily by setting a `_strict` key on the table to
--- false. Also adds a `global` table to the indexing chain that acts as a thin
--- wrapper around rawset.
local strict = function(env)
  local env = env or _G
  if env._strict ~= nil then
    return
  end
  env._strict = true

  local envmt = getmetatable(env) or {}
  local envindex = {}

  if envmt.__index or envmt.__newindex then
    error("__index or __newindex metaevents already bound", 2)
  end

  --- syntactical sugar for rawset
  envindex.global = setmetatable({}, {
    __index = env,
    __newindex = function(gl, name, value)
      rawset(env, name, value)
    end
  })

  envmt.__index = function(g, name)
    return (
      rawget(g, name) or envindex[name]
    ) or (
      g._strict and error(string.format(
        "attempt to get undeclared name '%s'", name
      ), 2)
    )
  end
  envmt.__newindex = function(g, name, value)
    if g._strict then
      error(string.format(
        "attempt to set undeclared name '%s'", name
      ), 2)
    else 
      rawset(g, name, value)
    end
  end
  setmetatable(env, envmt)
end
return strict

--- @example
require("strict")(_G)
global. foo = "foo"
foo = "bar"
_strict = false
foo = "baz"
_strict = true