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Lua metatable

A metatable is a special table that changes how another table behaves.

Core idea

Every table can have metatable

1
setmetatable(table, metatable)

Demo

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local defaults = {
    color = "red"
}

local obj = {
    size = 10
}

setmetatable(obj, {
    __index = defaults
})

print(obj.size)   -- 10 (from obj)
print(obj.color)  -- red (fallback to defaults)

__index

__index is a special field in a metatable that tells Lua:

If a key is not found in this table, look somewhere else