http://qs321.pair.com?node_id=302325


in reply to Re: How's your Perl?
in thread How's your Perl?

Though I'm almost certain that's what the OP had in mind, it relies on a bug rather than a documented feaure. For that reason I happen to like this solution to question #5 of the OP's quiz: 

sub{my$x=\$x};

[download]

Updated version that creates only one $x: 

sub { my $x; $x = \$x; }

[download]

The anonymous sub is created and immediately falls out of existance because it's not passed to a scalar variable. And yet $x never disappears because its reference count is always going to be 1; it refers to itself.

It probably doesn't qualify as a static, and is pretty much useless, but it meets the definition of static that the OP gave.


Dave


"If I had my life to live over again, I'd be a plumber." -- Albert Einstein

Replies are listed 'Best First'.
Re[3]: How's your Perl?
by xmath (Hermit) on Oct 27, 2003 at 06:36 UTC
    oops, you're right, my definition of "static" in the clarification was flawed :-)

    I do mean function-scoped static like in C/C++ ofcourse

    btw tachyon, your #1 solution isn't:
    perl -le 'my @x = ( \$_, \$_ ); $x[0]=42; print $x[1]'

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[d/l]

      Read your rules. You don't specify HOW the value of $x[0] is changed :-) vis Create an array @x such that changing $x[0] also sets $x[1] to the same value While assignment is one way to change a value.... 

      @x=(\$_,\$_);
$_=10;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
$_=20;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
__DATA__
$x[0] = 10
$x[1] = 10
$x[0] = 20
$x[1] = 20

      [download]

      cheers $[

      tachyon

      s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

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[d/l]
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        Create an array @x such that changing $x[0] ... 

        @x=(\$_,\$_);
my $initial_value = $x[0];
$_=10;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;
$_=20;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;

        [download]

        You're really printing the wrong thing. 

        print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
                 ^^      ^
LHS is $foo, RHS is $$foo. The output is very misleading.

print "\${\$x[$_]} = ${$x[$_]}\n" for 0..$#x;

LHS is $$foo and RHS is $$foo. But we're interested in $foo.

print "\$x[$_] = $x[$_]\n" for 0..$#x;

LHS is $foo and RHS is $foo. Output is correct and shows that the need
+ed change did not happen.

        [download]

        You're changing the variable that is refered to by the references in $x[0] and $x[1], but you're not actually changing the value in the container that is named $x[0].

        Clearer would be: "so that assigning to $x[0] also changes ...", but as said, we're against sanity.

        Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }

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[d/l]
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Re: Re: Re: How's your Perl?
by Anonymous Monk on Oct 27, 2003 at 04:27 UTC
    I do not think your code does what you think it does. You have two different $x variables shown in your anonymous subroutine, not a single one referencing itself.
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[d/l]
Re: Re: Re: How's your Perl?
by Anonymous Monk on Oct 27, 2003 at 05:38 UTC
    A static variable in a subroutine context would be created only once and hold its value between invocations. You've created a circular reference in an uninvokable routine. Even if it weren't optimized away, of which I am uncertain, it bears no resemblance to a static variable.
[reply]
      You are correct, given the conventional definition of a static variable. But the Original Poster provided us with a test of expert Perl prowess, and went so far as to give us his expert definition of static:

      "static variable" means a variable with infinite lifetime...

      My solution meets his spec. In a rediculous way, of course... but then again it's a rediculous quiz.


      Dave


      "If I had my life to live over again, I'd be a plumber." -- Albert Einstein
[reply]
        But the Original Poster provided us with a test of expert Perl prowess, and went so far as to give us his expert definition of static

        ok ok I messed up; because I've had questions about what a "static variable" is (not all perl programmers are C programmers) so I added a quick clarification and got it wrong.. nobody's perfect

        no need to get sarcastic here

        My solution meets his spec. In a rediculous way, of course... but then again it's a rediculous quiz.
        true on both points   :-)
[reply]

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