Metatables in lua

[Codex NG]

I was reading up on Metatables in lua it really isn't that hard to understand.

I was thinking if i can return a value from a method or function why can't I do that with a metatable

So I created a function that creates a very basic metatable

function createBasicMetatable()
    local x = setmetatable({ __index = {} },{
        __call = function(cls, ...)
            return cls.new(...)
        end,
    })
    function x.new()
        local self = setmetatable({}, x)
        return self
    end
    return x
end

Then just to run a test I took a string variable and tested the type

local var = "this is a string"
print(type(var))
-- string

Then i called createBasicMetatable() to return the metatable and store it in var and tested the type again

var = createBasicMetatable()
print(type(var))
-- now it prints table

So i wanted to see how this could be useful, so i gave var a property and gave it a value

var.aprop = 20

I wanted to check if aprop was truely a property of the var metatable
So I created a metamethod for var and used its new property

    function var:addThis(b)
        return self.aprop + b
    end

Then to test everything i called the var's metamethod, var's property and checked its type

print(type(var), var:addThis(6), var.aprop)
--output
-- table   26   20

I think this just might be an easier way for people to generate metatables

 

[Codex NG]

To expand upon this the constructor or new metamethod doesn't need to be called within the createBasicMetatable function, this could be defined outside, it really doesn't matter which ever is your preference.

You could very well craft an entire metatable inside the createBasicMetatable function and then call it as needed, this could very well be a template for all your 'objects'

I'll get more into a break down of how a metatable works in comparison to say a php class.

 

[Codex NG]

didn't work, got too excited :d

 

[dominus]

Very nice!