Lua Academy · Lesson

Creating Coroutines

Create coroutines with coroutine.create and coroutine.wrap.

What is a Coroutine?

A coroutine is a function that can pause its execution (yield) and later resume from where it left off. Unlike threads, coroutines are cooperative — only one runs at a time, and they explicitly yield control. Lua coroutines have their own stack and local variables.

local co = coroutine.create(function()
  print("start")
  coroutine.yield()
  print("resumed")
  coroutine.yield()
  print("done")
end)

print(coroutine.status(co))   -- suspended
coroutine.resume(co)          -- start
print(coroutine.status(co))   -- suspended
coroutine.resume(co)          -- resumed

coroutine.create vs coroutine.wrap

coroutine.create(fn) creates a coroutine and returns a coroutine object (type thread). coroutine.wrap(fn) creates a coroutine and returns a function that, when called, resumes it. wrap is simpler but hides the coroutine object.

-- create: returns coroutine object
local co = coroutine.create(function(x)
  return x * 2
end)
local ok, val = coroutine.resume(co, 5)
print(ok, val)   -- true  10

-- wrap: returns a resumable function
local gen = coroutine.wrap(function(x)
  return x * 3
end)
print(gen(5))    -- 15

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