engine.lua and car.lua are two modules. car accesses engine and provides access of it's state to engine using dependency injection. engine.lua on require statements uses different metatable than when later called with new().

engine.lua

-- engine.lua:

local Engine = {}
Engine.__index = Engine
Engine.__call = Engine.run

Engine.new = function(car)
    -- for dependency injection
    Engine.car = car
    local self = setmetatable({}, Engine)
    return self
end

Engine.run = function(self, opts) 
    print(self.car.name)
end

return setmetatable(Engine, { __call = Engine.new })

car.lua:

-- car.lua

local Car = {name = "ferrari"}
local Engine = require('engine') 
-- since in metatable __call = Engine.new

Car.run = Engine(Car)

-- now Engine is metatable for new object
-- so __call = Engine.run
local opts = {}
Car.run(opts)

when I run car.lua, I get: attempt to call field 'run' (a table value). On printing metatable of Car.run I see there is no __call method in metatable. Shouldn't it be there, since it is a key of Engine? why am I not able to call it?