Re: Optional attributes



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From: Shane Sendall (sendall@acm.org)
Date: Tue 18 May 2004 - 16:42:39 BST


Hi Laurie,
It is interesting that you differentiate between "never been 
initialized" and "uninitialized". Can you whet our appetitte further by 
giving us some examples of where you use this, i.e., some motivating 
examples?

Thanks,
    Shane
Laurence Tratt wrote:

><snip>
>Most languages that I am aware of do not, at the user level, differentiate
>between "this value has NULL assigned to it" and "this value is undefined" -
>NULL is all that is given to the user. Note that I am aware of several
>languages which *internally* have a way of noticing that certain variables
>and slots have not yet been assigned to, but there's no way for the user to
>test for this other than causing an exception to be generated. Certainly, my
>own Converge language follows in these footsteps, so that I can detect
>people attempting to read from variables before they have been assigned an
>initial value. Once an initial value has been assigned (be it NULL or
>anything else), it is impossible for the variable to return to the
>"undefined" state.
>
>Yours,
>
>
>Laurie
>  
>

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