编写模块

--- trim: a string-trimming module for Lua
-- Author, date, perhaps a nice license too
--
-- The code here is taken or adapted from  material in
-- Programming in Lua, 3rd ed., Roberto Ierusalimschy

-- trim_all(string) => return string with white space trimmed on both sides 
local trim_all = function (s)
  return (string.gsub(s, "^%s*(.-)%s*$", "%1"))
end

-- trim_left(string) => return string with white space trimmed on left side only
local trim_left = function (s)
  return (string.gsub(s, "^%s*(.*)$", "%1"))
end

-- trim_right(string) => return string with white space trimmed on right side only
local trim_right = function (s)
  return (string.gsub(s, "^(.-)%s*$", "%1"))
end

-- Return a table containing the functions created by this module
return {
  trim_all = trim_all,
  trim_left = trim_left,
  trim_right = trim_right
}

上述方法的另一种方法是创建顶级表，然后将函数直接存储在其中。在那个成语中，我们上面的模块看起来像这样：

-- A conventional name for the table that will hold our functions
local M = {}

-- M.trim_all(string) => return string with white space trimmed on both sides
function M.trim_all(s)
  return (string.gsub(s, "^%s*(.-)%s*$", "%1"))
end

-- M.trim_left(string) => return string with white space trimmed on left side only
function M.trim_left(s)
  return (string.gsub(s, "^%s*(.*)$", "%1"))
end

-- trim_right(string) => return string with white space trimmed on right side only
function M.trim_right(s)
  return (string.gsub(s, "^(.-)%s*$", "%1"))
end

return M

从调用者的角度来看，这两种风格之间几乎没有区别。 （值得一提的另一个区别是第一种风格使用户更难以对模块进行 monkeypatch。这可能是 pro 或 con，取决于你的观点。有关这方面的更多细节，请参阅 EnriqueGarcía 的这篇博客文章科塔）。