Re: Safe navigation operator

[Matthew Wild <mwild1@...>]

On 23 August 2010 13:25, Cuero Bugot <cbugot@sierrawireless.com> wrote:
>> Actually it is:
>>    debug.setmetatable(nil, { __index = {} })
>> You could turn this into a function to turn the feature on and off for
>> certain sections of code.
>
> Indeed this is a way to do it, but it is rather intrusive :) The fact is that I cannot isolate part of the code need this "safe navigation operator" or not, since it is usually embedded in the code here and there.
>

Maybe it's intrusive, maybe not. I've been toying with the idea of
making it default in my application. Thinking logically though:

1) That there is any code that relies on nil indexing throwing an
error is rather unlikely, because it's a very inconvenient place to
throw an error, especially as there is no way from the error to tell
where in the chain the nil was found.

2) If the code doesn't check each stage then it makes no substantial
difference whether the first or the last index in the chain returns
nil. With this metatable hack it will always act as if it was the last
that returned nil, that's all.

3) No other aspect of nil is changed, so using it in other places will
still trigger an error (trying to call it for example). As an aside,
adding a __call to nil would be something I /did/ disagree with,
because function calls are expected to *do something*.

4) Code that is already checking each individual step of the index
chain remains unaffected by the change.

5) As far as I can see this is the only "real" solution to your
problem. You want to be able to index a nil value, and Lua provides
you with a way to do exactly that.

However all this said, I still haven't enabled it in my code. Maybe
I'm just a chicken :)

Matthew