Perl noob here... I thought I understood the @_ array and its purpose with subroutines but then I found these usages that made run here for answers.. 
Readonly::Hash my %hash => (data => $data);
const my $min => 1;
const my $max => 10;
open (my $infile, '<', "datafile");
chomp(my $line = <STDIN>);

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Now I read and experimented and arrived at the simple subroutine below which reproduces the above but it makes me raise a simple question - What kind of Perl voodoo is happening when you pass my $num to a subroutine parameter list? 
sub doIt {
  $_[0] = $_[1];
}

doIt my $num => 4143;

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So what is happening with the @_?

In reply to The @_ array and the lexical variables by G4143

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