Volt Documentation

Sets an upvalue in a function by index.

Syntax

debug.setupvalue(func: function | number, index: number, value: any) -> void

Parameters

Parameter	Type	Description
`func`	`function` or `number`	The function or stack level
`index`	`number`	The upvalue index (1-based)
`value`	`any`	The new value for the upvalue

Returns

This function does not return a value.

Description

debug.setupvalue modifies an upvalue (captured variable) in a function. Changes affect the shared variable, so all functions that capture the same upvalue will see the change.

Example

local count = 0

local function getCount()
    return count
end

local function increment()
    count = count + 1
end

print(getCount()) -- 0

-- Directly modify the upvalue
debug.setupvalue(getCount, 1, 100)

print(getCount()) -- 100
increment()
print(getCount()) -- 101

Shared Upvalues

When multiple functions share an upvalue, modifying it affects all of them:

local shared = "original"

local function read()
    return shared
end

local function write(val)
    shared = val
end

-- Both functions share the same upvalue
debug.setupvalue(read, 1, "modified")

print(read())  -- "modified"
print(write)   -- The write function also sees the change

debug.getupvalue - Get an upvalue
debug.getupvalues - Get all upvalues

debug.setupvalue