why does removing "use 5.010;" break this?

bairdbe has asked for the wisdom of the Perl Monks concerning the following question:

I'm learning perl 5 by working through Learning Perl 6th ed. Why does removing line "Use 5.010;" break this? I'm use 5.18.2 of the compiler.

#!/usr/bin/perl
use strict;
use warnings;
use 5.010;

running_sum( 5, 6 );
running_sum( 1..6 );
running_sum( 4 );

sub running_sum {
    state $sum = 0;
    state @numbers;

    foreach my $number ( @_ ) {
        push @numbers, $number;
        $sum += $number;
    }

say "The sum of (@numbers) is $sum";
}
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Comment on why does removing "use 5.010;" break this? Download Code

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Re: why does removing "use 5.010;" break this? by 1nickt (Canon) on Oct 29, 2017 at 03:56 UTC
Hi, please put your code inside code tags. You can't use `state` or `say` as you have your code written, if you take out the `use 5.010` statement. As the documentation for state says: state is available only if the state feature is enabled or if it is prefixed with CORE:: . The state feature is enabled automatically with a use v5.10 (or higher) declaration in the current scope So you need to do one of: `use 5.010;` `use feature 'state';` `CORE::state $foo = 'bar';` Hope this helps! The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re: why does removing "use 5.010;" break this? by haukex (Archbishop) on Oct 29, 2017 at 06:45 UTC
say and state are "features" that need to be explicitly enabled, either with `use feature qw/say state/;`, but also use with only a version number will enable the "feature bundle" associated with that Perl version, which for v5.10 happens to be "`say state switch`" (Update: Forgot `array_base`, since it wasn't added until v5.16, thanks for the reminder ikegami).	[reply] [d/l] [select]
Re: why does removing "use 5.010;" break this? by ikegami (Patriarch) on Oct 29, 2017 at 18:10 UTC
`use 5.010;` [download] is equivalent to `BEGIN { $] >= 5.010 or die "Perl v5.10.0 required--this is only $^V, stopped"; } use feature qw( :5.10 );` [download] which is equivalent to `BEGIN { $] >= 5.010 or die "Perl v5.10.0 required--this is only $^V, stopped"; } use feature qw( array_base say state switch );` [download] Your program relies on the `say` and `state` features being activated, so if you remove `use 5.010;`, you need to add `use feature qw( say state );` instead. Note that those features were introduced in 5.10, so switching wouldn't gain you anything.	[reply] [d/l] [select]