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Do you know where your variables are?

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( #3333=superdoc: print w/replies, xml ) Need Help??
This is from the Perl Cookbook Recipe 11.17 (Program: Binary Trees).
#!/usr/bin/perl use strict; use Data::Dumper; my $root; insert( $root, 5 ); insert( $root, 3 ); print Dumper \$root; sub insert { my ($tree, $value) = @_; unless ($tree) { $tree = {}; $tree->{VALUE} = $value; $tree->{LEFT} = undef; $tree->{RIGHT} = undef; $_[0] = $tree; # $_[0] is reference param! return; } if ( $tree->{VALUE} > $value ) { insert( $tree->{LEFT}, $value ) } elsif ( $tree->{VALUE} < $value ) { insert( $tree->{RIGHT}, $value + ) }; }
I am trying to understand the relevance of this line:
$_[0] = $tree;
He mentioned that this is a reference param. And also he mentioned that "The assignment of the new node back to $_[0] alters the value in its caller."

But I still don't get it. If I removed this line, I don't get any output.

I ran the debugger but to no avail, I still could not figure out what is the relevance of that line. Why did he write it? And is there another way to write it maybe a longer version?

Can someone help understand this? Thanks.

In reply to Binary Search Tree Debug Question by bichonfrise74

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