Perl 101: Things Every Perl Programmer Should Know.


References are scalars that refer to other variables

References are like pointers in C in that they refer to other variables. Create a reference with the \ operator.

    my $sref = \$scalar;
    my $aref = \@array;
    my $href = \%hash;
    my $cref = \&subroutine;

The thing the reference point to is the "referent".

Dereference a reference with the appropriate sigil, preferably in squiggly braces.

    my $other_scalar = ${$sref};
    my @other_array  = @{$aref};
    my %other_hash   = %{$href};
    &{$cref} # Call the referent.

Arrow pointer is easier way to dereference.

To access array and hashrefs, use the -> operator.

    my $stooge = $aref->[1];
    my $stooge = $href->{Curly};

ref vs isa

  • A reference belongs to one class
  • You can check this class with ref
  • An object reference can inherit from other classes
  • You can ask an object if it inherited from a class with isa
  • Don't use ref without a good reason
  • isa is part of the UNIVERSAL package, so you can call it on objects
        my $mech = WWW::Mechanize->new;
        print "ok\n" if $mech->isa('LWP::UserAgent');

References to anonymous subroutines

Subroutines can be assigned to a variable, then called, allowing code references to be passed around and used at will. This can come in handy if, for example, you're writing a subroutine that needs to execute supplied code as part of its work.

    my $casefix = sub { return ucfirst lc $_[0] };

    my $color = $casefix->("rED");
    print "Color: $color\n"; # prints Red


Arrays of arrayrefs, hashes of hashrefs

perldoc perlreftut

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