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Re: Curious about Hashes which viewed as a list has only one item

by Errto (Vicar)
on Feb 29, 2008 at 00:03 UTC ( #671057=note: print w/replies, xml ) Need Help??

in reply to Curious about Hashes which viewed as a list has only one item

It's a key, with the undefined value as its corresponding value. If you have warnings enabled you'll get a warning "Odd number of elements in hash assignment"

If you use that hash in list context you'll get a list of a single element which contains that string HASH... By the way, note that it is a string, it's not an actual reference. The reason is that in Perl, hash keys are always treated as strings; other scalars (numbers, references, undef) are stringified when you use them as a hash key.

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Re^2: Curious about Hashes which viewed as a list has only one item
by ack (Deacon) on Feb 29, 2008 at 05:28 UTC

    Thanks, errto. That was what I suspected would be the case. So do I understand correctly that if I were to do something like:

    print "yep" if(defined $foo{HASH(xxx)});

    then I'd not expect any print? (The xxx is the stringified octal code in the pre-stringified reference)

    Also, thanks for the note on the stringified reference. I remember well (from having made the erroneous assumption quite a few times) that the key is just the stringified version of the reference and is not, itself, a referene.

    Again, thanks for the really helped.

    ack Albuquerque, NM
      Well, for one thing if you were actually writing that literally you'd have to put the HASH(xxx) bit in quotes. But you're correct, that statement would not print anything. But if you changed defined to exists, then it would print yep because that key is really present in the hash.

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[Corion]: Maybe I can still find something that is compatible with handlebars.js (which has JS precompilation) but allows for two-way data binding (which is great for the UI)
[Corion]: Two-way data binding means that if you change something in a text box, the corresponding variable in your Javascript gets updated immediately as well, and if you then change the variable, the corresponding text box also gets updated
[Corion]: That is a horrible approach that was also taken by Access, but if you have hooks that prevent automatic saving to the database, it is incredibly handy

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