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Re^5: Occurence List

by Anique (Acolyte)
on Oct 11, 2012 at 11:45 UTC ( #998419=note: print w/ replies, xml ) Need Help??


in reply to Re^4: Occurence List
in thread Occurence List

when you write

$ perl -le " use warnings; use strict; my $foo; $foo++; print $foo " 1

you declare $foo by saying my $foo; and then do something with it($foo++). Of course $foo++ would then not cause autovivication, because $foo already exists.

The thing with array indexes and hash keys, is that we do not have to declare them before we can use them. There is no need to say my $bar[396];, or even my $bar[396]++; before you can assign anything to it.


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Re^6: Occurence List (more on autovivification)
by Anonymous Monk on Oct 12, 2012 at 07:26 UTC

    Can you cite your sources? Where did you learn about autovivification? in perl?

    You offered these two snippets but they're not perl :)

    $ perl -le " my $bar[396]++; " syntax error at -e line 1, near "$bar[" Execution of -e aborted due to compilation errors. $ perl -le " my $bar[396]; " syntax error at -e line 1, near "$bar[" Execution of -e aborted due to compilation errors.

    $foo is a named variable, it has a name, it doesn't need to be autovified, it exists by virtue of being named, just like @bar is a named variable, it has a name, it doesn't need to be autovivified, it exists by virtue of being named. By default all variables are global.

    When you add my $foo; my @bar; you declare $foo and @bar to be lexical variables (not global)

    it also has the side effect of satisfying use strict 'vars'; by letting it know you didn't make a typo, that you intended to have variables named $foo and @bar

    neither is related to what we call autovivification ; autovivification is about using references to create complex data structures with less clicks of the keyboard

    autovivification does not refer to declaring (naming) variables, it is a feature that saves you typing, it saves you from having to write  $foo[6] ||= []; $foo[6][6]=6; you can simply write  $foo[6][6] = 6; and  $foo[6] autovivifies/ becomes an arrayref

    explicit, assigning an array ref to  $foo[6] ||= []; $foo[6][6]=6;

    implicit, autovivifying an array ref, treat it like an array ref, it becomes an array ref  $foo[6][6] = 6;

    autovivification, autovivification, The Bad, the Ugly, and the Good of autovivification, References quick reference, autovivification, autovivification, undefined value as an ARRAY reference sometimes ok, What does Autovivify mean?, Should perl auto vivify here?, Tutorials ...

      Thank you for further explaining autovivication to me. However, I would like to note that I said not to use the two snippets you quoted. I am not surprised they result in a syntax error :)

        Thank you for further explaining autovivication to me. However, I would like to note that I said not to use the two snippets you quoted.

        Actually you said "do not have to" and "no need to" and that is different from "not to" (shouldn't)

        I am not surprised they result in a syntax error :)

        "I believe you" :)

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