Lua Academy · Lesson

Module Patterns and Best Practices

Use local M = {} pattern and expose public API cleanly.

The M = {} Pattern

The universal Lua module pattern: declare a local table, populate it, return it. All public symbols go in M; all private helpers are plain locals. This is clear, minimal, and works everywhere.

-- The canonical module pattern
local M = {}

-- Private helper (not exported)
local function validate(x)
  return type(x) == "number" and x >= 0
end

-- Public API
function M.sqrt(x)
  assert(validate(x), "expected non-negative number")
  return math.sqrt(x)
end

M.PI = math.pi

return M

Self-Referential Module

Inside a module, functions can call other module functions either by name (M.foo()) or as locals. Using locals is slightly faster; using M.foo() allows users to override M.foo and have the internal call use the override (monkey patching).

local M = {}

-- Option A: use M.foo inside (allows override)
function M.double(n) return M.multiply(n, 2) end
function M.multiply(a, b) return a * b end

-- Option B: use local function (faster, no override)
local function mul(a, b) return a * b end
function M.triple(n) return mul(n, 3) end

return M

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