[Guide] Lua Allgemeines, Metatables, Metamethods (fortgeschrittener Guide)

Code:

local meta = {
	__index = function(tbl, key)
		return key
	end
}
local names = {sensi = "Felix", akkelos = "Laurin"}
setmetatable(names, meta)

print(names.sensi)
print(names.akkelos)
print(names.yiv)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
Felix
Laurin
yiv
>

Alternativ: Hinterlegen eines Tables:

Code:

local names2 = {yiv = "Faggot#2"}
local meta = {
	__index = names2
}
local names = {sensi = "Felix", akkelos = "Laurin"}
setmetatable(names, meta)

print(names.sensi)
print(names.akkelos)
print(names.yiv)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
Felix
Laurin
Faggot#2
>

Code:

local meta = {
	__newindex = function(tbl, key, value)
		print(string.format("creating new index (%s) on %s: %s", tostring(key), tostring(tbl), tostring(value)))
	end
}
local names = {sensi = "Felix", akkelos = "Laurin"}
setmetatable(names, meta)

names.yiv = "Faggot#2"

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
creating new index (yiv) on table: 00000000007E14F0: Faggot#2
>

Code:

local meta = {
	__mode = "v"
}
local names = {}
setmetatable(names, meta)

if true then
	local x = {}
	names[1] = x
end

collectgarbage()

print(names[1])

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
nil
>

Code:

local meta = {
	__call = function(tbl, ...)
		for k,v in ipairs(arg) do
			table.insert(tbl, v)
		end
	end
}
local names = {}
setmetatable(names, meta)

names("Felix", "Laurin", "Faggot#2")

for k,v in ipairs(names) do
	print(v)
end

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
Felix
Laurin
Faggot#2
>

Code:

local meta = {
	__metatable = "xd",
}
local names = {}
setmetatable(names, meta)

print(getmetatable(names))

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
xd
>

Code:

local meta = {
	__tostring = function(tbl)
		local str = ""
		
		for k,v in ipairs(tbl) do
			str = str .. (str == "" and "" or ", ") .. v
		end
		
		return "{" .. str .. "}"
	end
}
local names = {"Felix", "Laurin"}
setmetatable(names, meta)

print(names)--tostring wird hier automatisch aufgerufen

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
{Felix, Laurin}
>

Code:

local meta = {
	__len = function(tbl)
		local length = 0
		
		for k,v in ipairs(tbl) do
			length = length + string.len(tostring(v))
		end
		
		return length
	end
}
local names = {"Felix", "Laurin"}
setmetatable(names, meta)

print(#names)

Code:

Lua 5.5.1  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
11
>

Code:

if true then
	local meta = {
		__gc = function(tbl)
			_G.__BACKUP__ = {}
			
			for k,v in ipairs(tbl) do
				table.insert(_G.__BACKUP__, v)
			end
		end
	}
	local names = {"Felix", "Laurin"}
	setmetatable(names, meta)
end

collectgarbage()

for k,v in ipairs(_G.__BACKUP__) do
	print(v)
end

Code:

Lua 5.5.1  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
Felix
Laurin
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end


local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__unm = function(tbl)
		return -(tbl + 0)
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print(-tbl)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
-31
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end


local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print(tbl + 10)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
41
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end


local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__sub = function(operand1, operand2)
		return (operand1 + 0) - (operand2 + 0)
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print(tbl - 10)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
21
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end


local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__mul = function(operand1, operand2)
		return (operand1 + 0) * (operand2 + 0)
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print(tbl * 10)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
310
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end


local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__div = function(operand1, operand2)
		return (operand1 + 0) / (operand2 + 0)
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print(tbl / 10)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
3.1
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end


local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__pow = function(operand1, operand2)
		return (operand1 + 0) ^ (operand2 + 0)
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print(tbl ^ 10)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
8.196282869808e+014
>

Code:

local meta = {
	__tostring = function(tbl)
		local str = ""
		
		for k,v in ipairs(tbl) do
			str = str .. (str == "" and "" or ", ") .. v
		end
		
		return "{" .. str .. "}"
	end,
	__concat = function(str1, str2)
		return tostring(str1) .. tostring(str2)
	end
}
local tbl = {1, 10, 20}
setmetatable(tbl, meta)

print("tbl: " .. tbl)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
tbl: {1, 10, 20}
>

Code:

local meta = {
	__eq = function(operand1, operand2)
		for i = 1, table.getn(operand1) do
			if operand1[i] ~= operand2[i] then
				return false
			end
		end
		
		return true
	end,
}
local tbl1 = {1, 10, 20}
local tbl2 = {1, 10, 20}
local tbl3 = {1, 10}
setmetatable(tbl1, meta)
setmetatable(tbl2, meta)
setmetatable(tbl3, meta)

print(tbl1 == tbl2)
print(tbl1 == tbl3)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
true
false
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end

local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__lt = function(operand1, operand2)
		return (operand1 + 0) < (operand2 + 0)
	end,
}
local tbl1 = {1, 10, 20}
local tbl2 = {1, 10, 20}
local tbl3 = {1, 10}
setmetatable(tbl1, meta)
setmetatable(tbl2, meta)
setmetatable(tbl3, meta)

print(tbl1 > tbl2)
print(tbl1 > tbl3)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
false
true
>

Code:

function sum(tbl)
	local value = 0
	
	for k,v in ipairs(tbl) do
		value = value + v
	end
	
	return value
end

local meta = {
	__indentifier = "META#2840214702",
	__add = function(operand1, operand2)
		local o1meta = getmetatable(operand1) or {}
		local o2meta = getmetatable(operand2) or {}
		
		if o1meta.__indentifier and o1meta.__indentifier == "META#2840214702" then
			operand1 = sum(operand1)
		end
		if o2meta.__indentifier and o2meta.__indentifier == "META#2840214702" then
			operand2 = sum(operand2)
		end
		
		return operand1 + operand2
	end,
	__le = function(operand1, operand2)
		return (operand1 + 0) <= (operand2 + 0)
	end,
}
local tbl1 = {1, 10, 20}
local tbl2 = {1, 10, 20}
local tbl3 = {1, 10}
setmetatable(tbl1, meta)
setmetatable(tbl2, meta)
setmetatable(tbl3, meta)

print(tbl1 >= tbl2)
print(tbl1 >= tbl3)

Code:

Lua 5.0.3  Copyright (C) 1994-2006 Tecgraf, PUC-Rio
> dofile("test2.lua")
true
true
>

Code:

local READONLY = {}

_G.__READONLY__ = setmetatable({}, {
	__index = READONLY,
	__newindex = function(tbl, key, value)
		if READONLY[key] ~= nil then
			error("attempt to modify read-only value")
			return
		end
		
		READONLY[key] = value
	end,
	__metatable = false
})

function readOnlyValue(name, value)
	_G.__READONLY__[name] = value
end






local _GmetaRef = getmetatable(_G) or {}

_GmetaRef.__index = function(tbl, key)
	return tbl.__READONLY__[key]
end

_GmetaRef.__newindex = function(tbl, key, value)
	if tbl.__READONLY__[key] ~= nil then
		error("attempt to modify read-only value")
		return
	end
	
	rawset(tbl, key, value)
end

setmetatable(_G, _GmetaRef)


readOnlyValue("test", "Hello World!")
print(test)
test1 = "x"
test = "x"