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4. Modules

1. Modules

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-- 4. Modules.
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-- Suppose the file mod.lua looks like this:
--[[
local m = {}

local function sayMyName()
  print("Hrunkner")
end

function m.sayHello()
  print("Why hello there")
  sayMyName()
end

return m
--]]

-- Another file can use mod.lua's functionality:
local mod = require("mod") -- Run the file mod.lua.

-- require is the standard way to include modules.
-- require acts like:     (if not cached; see below)
--[[
local mod = (function ()
  <contents of mod.lua>
end)()
--]]
-- It's like mod.lua is a function body, so that
-- locals inside mod.lua are invisible outside it.

-- This works because mod here = m in mod.lua:
mod.sayHello() -- Prints: Why hello there Hrunkner

-- This is wrong; sayMyName only exists in mod.lua:
mod.sayMyName() -- error

-- require's return values are cached so a file is
-- run at most once, even when require'd many times.

-- Suppose mod2.lua contains "print('Hi!')".
local a = require("mod2") -- Prints Hi!
local b = require("mod2") -- Doesn't print; a=b.

-- dofile is like require without caching:
dofile("mod2.lua") --> Hi!
dofile("mod2.lua") --> Hi! (runs it again)

-- loadfile loads a lua file but doesn't run it yet.
F = loadfile("mod2.lua") -- Call F() to run it.

-- load is loadfile for strings.
-- (loadstring is deprecated, use load instead)
G = load("print(343)") -- Returns a function.
G() -- Prints out 343; nothing printed before now.

References