Re^4: Easiest way to do something only on first iteration of loop

When it [a state variable] is "out of scope", then next time it comes into scope it is reinitialized.

Sorry to be pedantic, but no, as the documentation says, it is never reinitialized. Consider:

use strict;
use warnings;
use feature qw( say state );

my $x = 42;

for (1 .. 2)
{
    for (1 .. 3)
    {
        state $x;
        ++$x;
        say "\$x = $x";
    }

    say "state \$x is out of scope here";
    say "\$x = $x";
}
[download]

Output:

16:48 >perl 1626_SoPW.pl
$x = 1
$x = 2
$x = 3
state $x is out of scope here
$x = 42
$x = 4
$x = 5
$x = 6
state $x is out of scope here
$x = 42

16:48 >
[download]

When the inner for loop ends, state $x goes out of scope and the $x that is printed is the my $x with wider scope. But when the inner for loop is re-entered, the inner-scope $x (the state variable) retains the value it had previously: it is not reinitialized.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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Re^5: Easiest way to do something only on first iteration of loop by Marshall (Canon) on May 08, 2016 at 12:21 UTC
Athanasius Thank you for the correction! I played with your code and even if the for loops are in a subroutine, the state version of $x is never re-initialized. In the documentation, my brain got stuck when the first sentence compared it to a my variable, causing a brain cramping mis-reading of the rest! Great that we have more eyeballs than mine on this stuff! One thing I didn't test was behavior in threads. I am not sure what would happen.	[reply]
Re^6: Easiest way to do something only on first iteration of loop by BrowserUk (Patriarch) on May 08, 2016 at 12:48 UTC
One thing I didn't test was behavior in threads. I am not sure what would happen. As with all variables that are not explicitly shared, each thread gets its own copy of any state variable; but within that thread it performs consistently with its behaviour in 'non-threaded' (single-threaded) code as you would expect: `CC:\test>perl -Mthreads -E" async{ for(1..4){ state $x = 123; say thre +ads->tid, ':', $x++ } }->join for 1 .. 4" 1:123 1:124 1:125 1:126 2:123 2:124 2:125 2:126 3:123 3:124 3:125 3:126 4:123 4:124 4:125 4:126` [download] With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :) In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]