userdata

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userdata#

A userdata value is a block of memory owned by C code, exposed to Lua through the C API. The operator meets userdata inside hosts that wrap their own objects: a Wireshark Pinfo, an Nmap Target, a LuaSocket socket, an OpenResty request.

The operator does not create userdata in pure Lua; they call into the host and treat the returned value as opaque.

local socket = require("socket")
local s = socket.tcp()              -- s is a userdata
print(type(s))                      --> userdata

Userdata can carry a metatable (set by the host) so it behaves like an object with methods.

s:connect("example.com", 80)
s:send("GET / HTTP/1.0\r\n\r\n")
s:close()

References#

  • table for the in-Lua object pattern.

  • Libraries for the host APIs that expose userdata.

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