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debug.getupvalues

C closures are not supported

This function will throw an error if called on a C closure, such as print, for security reasons.

debug.getupvalues returns a list of upvalues captured by a Luau function. These are the external variables that a function closes over from its surrounding scope.

If the function has no upvalues, the result will be an empty table.

function debug.getupvalues(func: (...any) -> (...any) | number): { any }

Parameters

Parameter Description
func The Luau function (or stack level) to retrieve upvalues from.

Examples

Example 1

Retrieving upvalues from a closure
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local var1 = false
local var2 = "Hi"

local function dummy_function()
    var1 = true
    var2 ..= ", hello"
end

for index, value in pairs(debug.getupvalues(dummy_function)) do
    print(index, value)
end

-- Output:
-- 1 false
-- 2 Hi

Example 2

Calling with a function that has no upvalues
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local function dummy_function()
    return 123
end

print(next(debug.getupvalues(dummy_function))) -- Output: nil

Example 3

Calling on a C closure should error
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print(debug.getupvalues(print)) -- Should error due to being a C closure