What is a alternative for python classes in lua? - python-3.x

Question

So i'm trying to convert python to lua but a road block i have right now is the class i'm not sure how i would convert a class to lua does anyone know how i would go about converting a class from python to lua?
python class
class

Answer 1

The OOP magic can be done with Lua tables and metatables.
Python
Look at The __init__() Function example here...
https://www.w3schools.com/python/python_classes.asp
Lets implement this with Lua...
( Lua 5.4 interactive console )
> _VERSION
Lua 5.4
> Person = setmetatable({},{
__call = function(self, name, age)
self.name = name
self.age = age
return {name = self.name, age = self.age}
end
})
> p1 = Person("John", 36)
> print(p1.name, p1.age)
John 36
So, some readers would ask: Why a metatabled table?
A simple function could do the same job.
Once a table has a metatable it is quit simple to add methods...
> Person = setmetatable({},{
__call = function(self, name, age)
self.name, self.age = name, age
table.insert(self, {name = self.name, age = self.age}) -- Numbered keys are the Data part
return {name = self.name, age = self.age}
end,
__index = {list = function(self) for i = 1, #self do print(self[i].name, self[i].age) end end}
})
> Person("John", 31);
> Person("Jack", 32);
> Person("Jim", 33);
> Person:list()
John 31
Jack 32
Jim 33
...that can handle the data of the table by itself.
Its a great benefit that the behaviour of a table can be controlled with metatables/methods.
And above example is only the tip of the iceberg.
Have a look at the __index of a string...
> for key, value in pairs(getmetatable(_VERSION).__index) do print(key, "=", value) end
byte = function: 0x565d6f20
lower = function: 0x565d4d90
len = function: 0x565d4750
sub = function: 0x565d7210
dump = function: 0x565d5d00
gsub = function: 0x565d7dc0
char = function: 0x565d5060
unpack = function: 0x565d6530
match = function: 0x565d7da0
packsize = function: 0x565d6420
pack = function: 0x565d6950
upper = function: 0x565d4ac0
format = function: 0x565d52d0
reverse = function: 0x565d4b50
find = function: 0x565d7db0
gmatch = function: 0x565d70d0
rep = function: 0x565d4be0
Therefore this is possible...
> print(("koyaanisqatsi"):upper():reverse())
ISTAQSINAAYOK
Means: Methods can be chained if their returning datatype has a method
Exceptions are: len() accept but dont return a string and sub() needs numbers before it returns a string also dump() needs a self defined function and returns a binary (almost unreadable) string.