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proxyud

proxyud creates a full userdata object, optionally associating a value to it, and setting a metatable to it. It's purpose is to be used as a proxy to another Lua object.

The returned proxy is not the value passed to new with the given metatable, which would be pointless, it's a new userdata which has the value associated to it, and with the given metatable.

Building

make should do the job. It will generate a shared object that can be required in Lua code.

Usage

proxyud.new

proxyud.new creates the userdata object:

proxyud.new(
    value,    -- Value that will be set as the userdata's user value, optional.

    metatable -- Metatable for the userdata object (optional, the object
              -- will not have a metatable if not informed).
)

Example:

local proxyud = require 'proxyud'

-- Initialized without a metatable.
local ud1 = proxyud.new(math.pi)
print(proxyud.get(ud1)) -- prints 3.1415926535898

-- Initialized with a metatable.
local ud2 = proxyud.new(math.pi, {
    __tostring = function(self)
        return tostring(proxyud.get(self))
    end,

    __call = function(self)
        print(proxyud.get(self))
    end
})

print(ud2) -- prints 3.1415926535898
ud2() -- prints 3.1415926535898

-- Initialized with a metatable.
local ud3 = proxyud.new({pi = math.pi}, {
    __index = function(self, key)
        return proxyud.get(self)[key]
    end,

    __newindex = function(self, key, value)
        error('trying to modify a const table')
    end
})

print(ud3.pi) -- prints 3.1415926535898
print(ud3.notfound) -- prints nil
ud3.pi = 3 -- raises an error

proxyud.get

Does the same thing as debug.getuservalue, but checks if the argument is a full userdata. Convenience function for when the debug library is not available.

proxyud.identitymetatable

Returns a metatable that forwards all metamethods to the original object. Each call to proxyud.identitymetatable returns a new table.

The following metamethods are not present in the identity metatable:

  • __gc: This metamethod would call the original object's __gc, which would be called again when the original object is collected.
  • __mode: This is a string rather than a function, so it's not possible to make it return the value from the original object's metatable.
  • __name: Same as with __mode.

Changelog

  • 1.0.0
    • First public release
  • 1.1.0
    • Added proxyud.identitymetatable

License

MIT, enjoy.