Basic

_G
Description: Global variable that holds the global environment (all global functions/variables)
Example:
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print(_G.tostring(true)) -- tostring is global, which makes it accessible via _G as well
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setfenv
Description: sets the environment for a function to use, rather than _G.
Usage: setfenv(f)
Example:
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function x()
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    zzz.x = 5
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    print() -- will not work here, the environment is not _G.
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end
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​
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setfenv(x, {zzz = {x = 10}})
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getfenv
Description: returns the environment in use by given function or stack level, default 1.
Usage: getfenv([f])
Example:
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function x()
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    zzz.x = 5
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    print() -- will not work here, the environment is not _G.
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end
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​
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setfenv(x, {zzz = {x = 10}})
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print(getfenv(x)) -- environment is {zzz = {x = 10}}
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setmetatable
Description: sets the metatable for given table
Usage: setmetatable(table, metatable)
Example:
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local t = {}
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setmetatable(t, {__call = print})
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getmetatable
Description: gets the metatable of specified table, returning the __metatable metamethod's value if applicable
Usage: getmetatable(table)
Example:
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local t = {}
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setmetatable(t, {__call = print})
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print(getmetatable(t)) -- {__call = print}
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setmetatable(t, {__metatable = {x = 5}})
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print(getmetatable(t)) -- {x = 5}
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rawset
Description: sets a value in the table at specified index without invoking any metamethods
Usage: rawset(table, index, value)
Example:
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local t = {}
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setmetatable(t, {__newindex = function(self, k, v)
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    print('Value set at index '.. tostring(k) ..' to value '.. tostring(v))
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end})
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​
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t.x = 5 -- Value set at index x to value 5
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rawset(t, 'xx', 50) -- prints nothing, __newindex is not be invoked
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rawget
Description: returns a value from a table at given index without invoking any metamethods
Usage: rawget(table, index)
Example:
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local t = {}
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setmetatable(t, {__index = function(self, k, v)
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    print('Accessing value at index '.. tostring(k))
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end})
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​
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print(t.x) -- Accessing value at index x
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print(rawget(t, 'x')) -- nothing, __index is not invoked
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rawequal
Description: compares two values using == without invoking any metamethod
Usage: rawequal(v1, v2)
Example:
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local mt = {__eq = function(a, b)
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    print('Checking equality ( '.. tostring(a) ..' vs '.. tostring(b) ..' )')
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    return rawequal(a, b)
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end}
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​
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local t = {}
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setmetatable(t, mt)
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​
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local t2 = {}
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setmetatable(t2, mt)
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​
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print(t == t2) -- Checking equality ( table: 00f28b00 vs table: 00f28a10 )
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print(rawequal(t, t2)) -- nothing, __eq is not invoked
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pairs
Description: iterator to traverse over a table in any order possible
Usage: pairs(t)
Example:
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local t = {1, 2, 3}
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for k, v in pairs(t) do
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    print(k, v)
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end
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ipairs
Description: iterator to traverse over a table in sequence
Usage: ipairs(t)
Example:
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local t = {1, 2, 3}
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for k, v in ipairs(t) do
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    print(k, v)
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end
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loadstring
Description: loads a Lua chunk
Usage: loadstring(string [, chunkName])
Example:
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local f = loadstring([[return function() print(123) end]])
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f() -- 123
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loadfile
Description: loads a Lua chunk from specified file, or from standard input if filename is not specified
Usage: loadfile([filename])
Example:
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-- x.lua
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return function() print(123) end
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​
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-- other file.lua
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local f = loadfile("x.lua")
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f() -- 123
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next
Description: returns the next key, value pair in table starting from specified index, otherwise index, is nil
Usage: next(table [, index])
Example:
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local t = {1, 2, 3}
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print(next(t, 2)) -- 3, 3
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print(next(t)) -- 1, 1
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pcall
Description: calls a function in a protected state, returning any errors if they happen, otherwise returns true if successful plus the returned values from f
Usage: pcall(f, ...)
Example:
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function x(n)
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    return x + n
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end
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​
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local success, ret = pcall(x, 5)
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print(success, ret) -- false    C:\Users\user\lua_file.lua:2: attempt to perform arithmetic on a function value (global 'x')
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xpcall
Description: calls a function in a protected state, using err as the error handler and returning true if no errors happen, otherwise returns false plus the result from err
Usage: xpcall(f, err)
Example:
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function x(n)
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    return x + n
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end
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​
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local function x_error_handler(error)
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	print(error)
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	return 123
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end
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​
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local success, ret = xpcall(x, x_error_handler)
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print(success, ret)
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Output:
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C:\Users\user\lua_file.lua:2: attempt to perform arithmetic on a function value (global 'x')
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false 123
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unpack
Description: unpacks a table in sequence, starting from i and ending with j (1, #table respectively by default), returning all values from it
Usage: unpack(table [, i [, j]])
Example:
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local t = {1, 2, 3, 4, 5}
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print(unpack(t)) -- 1, 2, 3, 4, 5
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print(unpack(t, 2, 4)) -- 2, 3, 4
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type
Description: returns the data type of given value
Usage: type(value)
Example:
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print(type(123)) -- number
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print(type({})) -- table
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print(type(nil)) -- nil
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print(type('')) -- string
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print(type(true)) -- boolean
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tonumber
Description: converts value to a number if possible
Usage: tonumber(val [,base])
Example:
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local x = '5'
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print(tonumber(x)) -- 5
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print(type(tonumber(x))) -- number
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print(type(x)) -- string
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tostring
Description: converts value to a string
Usage: tostring(val)
Example:
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print(tostring({})) -- table: 00ee88a8
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print(tostring(5)) -- 5
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​
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print('This is a boolean: '.. tostring(true)) -- This is a boolean: true
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