Metatabele

local x = {}
local metaTable = {} -- Metatabele też są tabelami!
setmetatable(x, metaTable) -- Przypisz x metatabelę o nazwie metaTable!
print(getmetatable(x)) --> tabela: [adres pamięci w systemie szesnastkowym]

local x = {}
setmetatable(x, {})

local x = setmetatable({}, {})

local vector2 = {__type = "vector2"}
local mt = {__index = vector2}

function mt.__div(a, b)
	if type(a) == "number" then
		-- a to skalar, b to wektor
		local scalar, vector = a, b
		return vector2.new(scalar / vector.x, scalar / vector.y)
	elseif type(b) == "number" then
		-- a to wektor, b to skalar
		local vector, scalar = a, b
		return vector2.new(vector.x / scalar, vector.y / scalar)
	elseif (a.__type and a.__type == "vector2" and b.__type and b.__type == "vector2") then
		-- zarówno a, jak i b to wektory
		return vector2.new(a.x / b.x, a.y / b.y)
	end
end

function mt.__tostring(t)
	return t.x .. ", " .. t.y
end

function vector2.new(x, y)
	local self = setmetatable({}, mt)
	self.x = x or 0
	self.y = y or 0
	return self
end

local a = vector2.new(10, 5)
local b = vector2.new(-3, 4)

print(a / b) -- -3.3333333333333, 1.25
print(b / a) -- -0.3, 0.8
print(2 / a) -- 0.2, 0.4
print(a / 2) -- 5, 2.5

local metatable = {
	__unm = function(t) -- __unm jest dla operatora unarnego -
    local negated = {}
  	for key, value in t do
  		negated[key] = -value -- neguj wszystkie wartości w tej tabeli
  	end
  	return negated -- zwróć tabelę
	end
}

local table1 = setmetatable({10, 11, 12}, metatable)
print(table.concat(-table1, "; ")) --> -10; -11; -12

local metatable = {
	__index = {x = 1}
}

local t = setmetatable({}, metatable)
print(t.x) --> 1

local t = {10, 20, 30}
print(t(5))

local metatable = {
	__call = function(t, param)
	local sum = {}
		for i, value in ipairs(t) do
			sum[i] = value + param -- Dodaj argument (5) do wartości, a następnie umieść go w nowej tabeli (t).
		end
		return unpack(sum) -- Zwróć poszczególne wartości tabeli
	end
}

local t = setmetatable({10, 20, 30}, metatable)
print(t(5)) --> 15 25 35

local table1 = {10, 11, 12}
local table2 = {13, 14, 15}

for k, v in table1 + table2 do
	print(k, v)
end

local metatable = {
	__add = function(t1, t2)
		local sum = {}
		for key, value in t1 do
			sum[key] = value
		end

		for key, value in t2 do
			if sum[key] then
				sum[key] += value
			else
				sum[key] = value
			end
		end
		return sum
	end
}

local table1 = setmetatable({10, 11, 12}, metatable)
local table2 = setmetatable({13, 14, 15}, metatable)

for k, v in table1 + table2 do
	print(k, v)
end

local t = setmetatable({}, {
    __index = function(self, i)
    	self[i] = i * 10
    	return self[i]
    end,
    __newindex = function(self, i, v)
    	-- Nie ustawiaj wartości w tabeli w normalny sposób
    end
})
print(t[1]) -- Powoduje przepełnienie stosu

local t = setmetatable({}, {
	__index = function(self, i)
		rawset(self, i, i * 10)
		return self[i]
	end,
	__newindex = function(self, i, v)
		-- Nie ustawiaj wartości w tabeli w normalny sposób
	end
})
print(t[1]) --> 10

local Set = {}
Set.__index = Set

-- Funkcja do konstruowania zbioru z opcjonalnej listy przedmiotów
function Set.new(items)
	local newSet = {}
	for key, value in items or {} do
		newSet[value] = true
	end
	return setmetatable(newSet, Set)
end

-- Funkcja do dodania przedmiotu do zbioru
function Set:add(item)
	self[item] = true
end

-- Funkcja do usunięcia przedmiotu ze zbioru
function Set:remove(item)
	self[item] = nil
end

-- Funkcja do sprawdzenia, czy zbiór zawiera przedmiot
function Set:contains(item)
	return self[item] == true
end

-- Funkcja do wyjścia zbioru jako listy oddzielonej przecinkami do debugowania
function Set:output()
	local elems = {}
	for key, value in self do
		table.insert(elems, tostring(key))
	end
	print(table.concat(elems, ", "))
end

local fruits = Set.new({"Apple", "Lemon", "Orange", "Cherry", "Lime", "Peach"})

local fruits = Set.new({"Apple", "Lemon", "Orange", "Cherry", "Lime", "Peach"})
fruits:add("Mango")

local fruits = Set.new({"Apple", "Lemon", "Orange", "Cherry", "Lime", "Peach"})
fruits:remove("Orange")

local fruits = Set.new({"Apple", "Lemon", "Orange", "Cherry", "Lime", "Peach"})

local result1 = fruits:contains("Cherry")
print(result1) -- true

local result2 = fruits:contains("Watermelon")
print(result2) -- false

local function getIntersection(set1, set2)
	local result = Set.new()
	for key, value in set1 do
		if set2:contains(key) then
			result:add(key)
		end
	end
	return result
end

local freshFruits = Set.new({"Mango", "Lemon", "Orange", "Cherry", "Lime", "Peach"})
local frozenFruits = Set.new({"Mango", "Peach", "Pineapple"})

local commonFruits = getIntersection(freshFruits, frozenFruits)
commonFruits:output() -- Mango, Peach

function Set:__add(otherSet)
	local result = Set.new()
	for entry in self do
		result[entry] = true
	end
	for entry in otherSet do
		result[entry] = true
	end
	return result
end

local sweetFruits = Set.new({"Apple", "Mango", "Cherry", "Peach"})
local sourFruits = Set.new({"Lemon", "Lime"})

local allFruits = sweetFruits + sourFruits
allFruits:output() -- Peach, Lime, Apple, Cherry, Lemon, Mango

function Set:__sub(otherSet)
	local result = Set.new()
	for entry in self do
		result[entry] = true
	end
	for entry in otherSet do
		result[entry] = nil
	end
	return result
end

local allFruits = Set.new({"Apple", "Lemon", "Mango", "Cherry", "Lime", "Peach"})
local sourFruits = Set.new({"Lemon", "Lime"})

local sweetFruits = allFruits - sourFruits
sweetFruits:output() -- Mango, Apple, Cherry, Peach