in reply to Text::ExtractWords exhibits incomprehensible behavior?

Consider:

use strict;
use warnings;

my @powers = map{undef} 0 .. 3;
my $x = 2;

powers ($x, @powers);
print("$x @powers\n");


sub powers {
    $_[$_] = $_[$_ - 1] * $_[0] for 1 .. @_ - 1;
}

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Prints:

2 4 8 16 32

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Perl effectively passes parameters by reference. Arrays and hashes get flattened so each element becomes a parameter.

Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond

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Re^2: Text::ExtractWords exhibits incomprehensible behavior?
by Danny (Chaplain) on Jun 16, 2024 at 21:56 UTC
    Or perhaps more clearly: 
    my $me = "old me";
s1($me);
print "$me\n";

sub s1 {
  $_[0] = "new me";
}

    [download]
    But it's customary to make local copies of the parameters like 'my $var = shift' so they don't get changed.
[reply]
[d/l]
      I had no idea this was possible.

      So, I could create a version of `trim` that was more `chomp`-like? 

      sub mytrim {
    $_[0] =~ s/^\s+|\s+$//g;
}
my $text = '  this could use a trim.      ';
mytrim $text;

      [download]
[reply]
[d/l]
        Yes, @_ is always an alias for the actual variables that were passed to the function. It's generally bad to modify the caller's variables, but in some cases it gives a nice performance boost.

        Since you're just learning this, you should also know that for-loops do the same thing, even if you declare the loop variable with 'my'. IMHO they should have made it so that 'for my' de-aliases the loop item, and a different syntax for the (more efficient) aliasing behavior. Perl didn't have an internal copy-on-write back then though, so this was probably done for efficiency even though it's a bit of a foot-gun. 

        sub modify_it {
  $_[0]= 11;
}

my $x= 10;
for my $y ($x) {
  modify_it($y);
}
say $x; // $x is now 11

        [download]
[reply]
[d/l]

In Section Seekers of Perl Wisdom