RE: Safe navigation operator

[Cuero Bugot <cbugot@...>]

> If you don't mind adding a pair of parenthesis (or quotes) to the end
> of the expression, you can get something pretty nice with __call :

Using Jerome's idea of trailing "()", I came to a minimalist way doing safe navigation:


local meta = {}
meta.__index=function(t, key)
    return setmetatable({path=t.path.."."..key}, meta)
end
meta.__newindex=function(t, key, value)
    print ("setter", t.path.."."..key, value)
end
meta.__call=function(t)
    return "getter "..t.path
end
config = setmetatable({path=""}, meta)



> =config.network.server.url()
getter  .network.server.url

> config.network.server.url = "someurl"
setter  .network.server.url     someurl

Of course then it still need the setter and the getter that will actually do the reading/writing in the actual config table, but that's easy :)





--------------------------------
Same, but does not even create a new table for each traversal level...
Drawback is that it is not 'thread safe', and '()' must not be forgotten or next access will be corrupted...

local meta = {}
meta.__index=function(t, key)
    t.path = t.path.."."..key
    return t
end
meta.__newindex=function(t, key, value)
    print ("setter", t.path.."."..key, value)
    t.path = ""
end
meta.__call=function(t)
    local p
    p, t.path = t.path, ""
    return "getter "..p
end
config = setmetatable({path=""}, meta)