Lua table proxy
Lua has index and newindex metamethods, but not a setindex or changeindex. This way you don't know whether a key was already set and it's been changed.
This is a simple solution that proxies a table so that exploits __newindex to set values to a subject instead of the proxy itself.
This way when a key is set, it's always a "new index" in the proxy.
proxy={} function proxy.new (subject) p={subject=subject} setmetatable(p, proxy) return p end function proxy:__index(key) print ("get", key) return rawget(self, 'subject')[key] end function proxy:__newindex(key, val) print ("set", key, val) subject = rawget (self, 'subject') subject[key] = val end
Example usage:
mytbl = {} container = proxy.new(mytbl) print(container.test) container.test = 'mytest' print(container.test) container.test = 'newtest' print(container.test)
Notice "set" is being printed twice whenever a key is set, that's right what we wanted.