RE: Autovivification

 
--

On Sat, 9 Nov 2002 23:22:45   
 Brent Dax wrote:
>Michael Lazzaro:
># Brent Dax wrote:
># > 
># > I was writing up some docs (in a perldoc-like style--we can always 
># > change the form later, but the content is important), and started 
># > working on documenting references.  I ended up with this bit:
># 
># I imagine (if there are no objections) that the general 
># perldoc writing style (booklike, informal) is probably 
># exactly what we want, yes?  We'll just break it up into 
># *much* smaller individual sections, so that only one concept 
># is being taught at a time.  Probably.
>
>OK.  I'm trying to do that in the stuff I'm writing.
>
># > =head3 Autovivification
># >     @{%anagrams{$key}}.push $word;
># >     $undefined_var[$idx]=$scalar;
># 
># Hmm, not a clue.  I could argue that one both ways.  Perhaps (thinking
># aloud) they only autovivify if you've explicitly called out 
># the exact type they store, but otherwise generate an 
># exception?  (Because it seems like the behavior would be 
># _very_ handy if you wanted it, and a real pain in the $#@ 
># when you invoked it unintentionally.)
># 
># So maybe if you previously declared them like this:
># 
>#    my \Array %anagrams;
>#    my \Array $undefined_var;
>
>I think that, if Perl can determine the type with virtually no
>ambiguity, it should autovivify. 

Actually, this behavior has already (mostly) been decided over in P6 
language. It was decided (and I agree) that the Perl 5 behavior of 
autovivifying references to the basic data types is the incorrect 
behavior, leading to a lot of bugs when dealing wityh complex data 
structures. So no autovifiying an untyped $undefined_var[$foo]

However, a question unanswered is whether or not this behavior is 
inappropriate when the data structure had been appropriately typed.

-Erik

 In this case, since we know they
>wanted an array (they used the @ explicitly), we'll autovivify an array.
>(I say "virtually no" because one could make the argument that you don't
>know if we wanted a standard array or a typed one.)
>
>--Brent Dax <[email protected]>
>@roles=map {"Parrot $_"} qw(embedding regexen Configure)
>
>Wire telegraph is a kind of a very, very long cat. You pull his tail in
>New York and his head is meowing in Los Angeles. And radio operates
>exactly the same way. The only difference is that there is no cat.
>    --Albert Einstein (explaining radio)
>
>


____________________________________________________________
Get 25MB of email storage with Lycos Mail Plus!
Sign up today -- http://www.mail.lycos.com/brandPage.shtml?pageId=plus