lua table - Lua 5.2 metatables and environment -


i've got structure this:

context = {   pi = math.pi,   sin = math.sin,   cos = math.cos,   tan = math.tan,   print = print }  modules = {   m1 = {     variables = { x = 1 },     update = function(self)       local _env = self.variables       x = 2       m2.x = 2     end   },   m2 = {     variables = { x = 1 },     update = function(self)       local _env = self.variables     end   } }  setmetatable(modules.m1, {__index = modules.m1.variables}) setmetatable(modules.m1.variables, {__index = context})  setmetatable(modules.m2, {__index = modules.m2.variables}) setmetatable(modules.m2.variables, {__index = context})  setmetatable(context, {__index = modules})

the idea users enter code ui , code pasted update functions of different modules, after local _env set. user-entered code should sandboxed. should able access few functions (the ones in context table) , contents of other modules. code in m1:update should able refer variables in m1.variables without qualifying them; variables in other modules (ie ones in m2.variables) should accessible qualifying them module name (ie m2.x).

but result this:

$ lua -i test.lua > = modules.m1.x 1 > = modules.m1.variables.x 1 > = modules.m2.x 1 > = modules.m2.variables.x 1 > = modules.m1:update() > = modules.m1.x 2 > = modules.m1.variables.x 2 > = modules.m2.x 2 > = modules.m2.variables.x 1

why modules.m2.variables.x not getting updated? , if, seems, modules.m2.x different modules.m2.variables.x, modules.m2.x coming from?

modules.m2.variables.x not getting updated because set __index metamethod (which used when retrieving non-existing key), not __newindex metamethod (which used when assigning value non-existent key), , result value stored in modules.m2.x table , not modules.m2.variables.x table intended.

if add __newindex in setmetatable(modules.m2, {__index = modules.m2.variables, __newindex = modules.m2.variables}), expected result.


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