Scope for more than one instance of one Required Module?

Getting Started Newbie Questions
#1

In Scene A, we require Module X twice by 2 local variables modA and modB:

 local modA = require("moduleX") local modB = require("moduleX") modA.new() modB.new() modA.printIt () modB.printIt ()

Module X looks like:

local M = {} function M.new () local count = 0 function M.printIt () count = count + 1 print("count = ", count) end end return M

I would have expected this to output “count = 1” twice as there are 2 versions of count each one local to modA and modB. But it prints “count = 1” and “count = 2”. So not sure what’s going on. Firstly why is this the case and secondly how to achieve the original expectation?

Many thanks.

#2

Lua doesn’t have classes and instances like other OO languages.  

The require function is for loading “libraries”, not classes.   It automatically prevents loading the same library twice – The second call to require is going to see that you’ve already required the library, and just return a reference to it.   ModA and ModB are just two “pointers” to the loaded library.

Hope this makes sense.  

#3

This is one way, using meta tables: https://www.youtube.com/watch?v=CYxMfVy5W00

Scene A:

[lua]local ModuleX = require(“moduleX”)

local modA = ModuleX.new()

local modB = ModuleX.new()

modA:printIt ()

modB:printIt ()[/lua]

moduleX:

[lua]local M = {}

local M_mt = { __index = M }

function M.new ()

local moduleProperties = {

count = 0

}

return setmetatable( moduleProperties, M_mt )

end

function M:printIt ()

self.count = self.count + 1

print("count = ", self.count)

end

return M[/lua]

#4

Sorry, forum butchered indenting.

#5

Ah ok, metatables. Thanks JonJonsson. Very clear explanation and video. Will give it a go.

#6

Lua doesn’t have classes and instances like other OO languages.  

The require function is for loading “libraries”, not classes.   It automatically prevents loading the same library twice – The second call to require is going to see that you’ve already required the library, and just return a reference to it.   ModA and ModB are just two “pointers” to the loaded library.

Hope this makes sense.  

#7

This is one way, using meta tables: https://www.youtube.com/watch?v=CYxMfVy5W00

Scene A:

[lua]local ModuleX = require(“moduleX”)

local modA = ModuleX.new()

local modB = ModuleX.new()

modA:printIt ()

modB:printIt ()[/lua]

moduleX:

[lua]local M = {}

local M_mt = { __index = M }

function M.new ()

local moduleProperties = {

count = 0

}

return setmetatable( moduleProperties, M_mt )

end

function M:printIt ()

self.count = self.count + 1

print("count = ", self.count)

end

return M[/lua]

#8

Sorry, forum butchered indenting.

#9

Ah ok, metatables. Thanks JonJonsson. Very clear explanation and video. Will give it a go.