newproxy

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Creates a zero-size "userdata" object, optionally with a sharable empty metatable.

proxy = newproxy(withmetatable)
      = newproxy(otherproxy)

Arguments

withmetatable

boolean - Whether or not to to create a metatable for the userdata.

otherproxy

userdata - If an object previously created by newproxy is passed, the new userdata will share that proxy's metatable.

Returns

proxy

userdata - A userdata proxy object.

Details

• This function is an undocumented part of the Lua 5.1 standard library.
• This function is used by the Secure Handlers framework as a way of providing handles to frames within the restricted environment.
• Objects created by this function can have a metatable with a __gc method installed to dispatch a function when the object is garbage collected.
  • When using finalizers it is strongly recommended to use a protected call barrier as any errors that escape a finalizer may crash the client.

local function OnObjectCollected_Protected()
    error("Collected!")
end

local function OnObjectCollected()
    -- All errors within 'OnObjectCollected_Protected' will be forwarded
    -- to the global error handler and will avoid crashing the client.
    securecallfunction(OnObjectCollected_Protected)
end

local object = newproxy(true)
getmetatable(object).__gc = OnObjectCollected

Patch changes

Patch 10.1.0 (2023-05-02): __gc finalizers will no longer spread taint back to any calling code that triggered the collection of an object.