Hi sundialsvc4,

It's a very cool feature of 5.10 which mimics the static variable of C.  State variables don't lose their data, even when they go out of scope, so you can use them for cases where you want data to persist, without having to use globals.

For example, to perform initialization only once the first time a subroutine is called, you could do this: 

#!/usr/bin/perl -w

use feature qw{ state };
use strict;
use warnings;

for (1..5) {
    some_sub();
}

sub some_sub {
    (state $b_initialized++) or initialize();
    print "Now doing the main work of some_sub() ...\n";
}


sub initialize {
    print "Initializing....\n";
    # ... etc ...
}

__END__

=== Output ===

Initializing....
Now doing the main work of some_sub() ...
Now doing the main work of some_sub() ...
Now doing the main work of some_sub() ...
Now doing the main work of some_sub() ...
Now doing the main work of some_sub() ...

[download]

Or to define a subroutine which returns a unique integer each time it's called: 

#!/usr/bin/perl -w

use feature qw{ state };
use strict;
use warnings;

for (1..5) {
    printf "Got the value %d\n", unique_integer();
}


sub unique_integer {
    return ++(state $ncalls);
}

__END__

=== Output ===

Got the value 1
Got the value 2
Got the value 3
Got the value 4
Got the value 5

[download]
s''(q.S:$/9=(T1';s;(..)(..);$..=substr+crypt($1,$2),2,3;eg;print$..$/

In reply to Re^2: Interesting: a genuine Perl-bug by liverpole
in thread Interesting: a genuine Perl-bug by locked_user sundialsvc4

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.