Re: How can one decide between 'not set' and 'not existing?

[Dimiter 'malkia' Stanev <malkia@...>]

You would have to invent a different nil for that reason, and check 
against it.

Somewhere

-- "function() end" would gurantee an unique value, differentiated from 
others, unless the VM merges it under one umbrella. Even them, maybe 
reusing coroutine might return you an unique value for the lifetime of 
the application (or something even simpler)

NULL = function() end
or
NULL = coroutine.create(function()end)

a.key = NULL

and then use NULL as your special null value.

On 7/23/2012 7:50 PM, meino.cramer@gmx.de wrote:
> Hi,
>
> Suppose one do
>
> a = { key = nil }
> print( a.key )
>
> => nil
>
> print( a.carkey )
>
> => nil
>
> It looks like setting a key in a hash with value nil is the
> same as if the key does not exist at all.
>
> How can I decide between both in a program?
> Is there a 'exists' function as in Perl?
>
> Best regards and thank you very much in advance for any help!
> mcc