In Perl, how do I pass a function as argument of another function?

argument-passing, function, oop, perl

Solution

You would want to pass a reference to the subroutine.

$menu->addItem("First Option", \&firstOptionFunction);

And your addItem method might look like this:

sub addItem { ## your logic may vary
    my ( $self, $option, $code ) = @_;
    if ( $option eq 'First Option' ) {
        $code->();
    }

    $self->{ITEM} = $option;
    push @MENU_ITEMS, $option;

    return;
}

As you mentioned in the comments, you might want to not pass the subroutine as a reference, but rather store it somewhere else. Something like this might work:

sub new {
    my $class = shift;
    my $self = bless {}, $class;
    $self->{f_o_code} = \&firstOptionFunction; ## use a better name than f_o_code
    return $self;
}

## add your other methods

sub addItem { ## your logic may vary
    my ( $self, $option ) = @_;
    if ( $option eq 'First Option' ) {
        $self->{f_o_code}->();
    }

    $self->{ITEM} = $option;
    push @MENU_ITEMS, $option;

    return;
} ## call like $menu->addItem( 'First Option' );

Problem

I wrote the following Perl Class: ``` package Menu; use strict; my @MENU_ITEMS; my $HEADER = "Pick one of the options below\n"; my $INPUT_REQUEST = "Type your selection: "; sub new { my $self = {}; $self->{ITEM} = undef; $self->{HEADER} = undef; $self->{INPUT_REQUEST} = undef; bless($self); return $self; } sub setHeader { my $self = shift; if(@_) { $self->{HEADER} = shift } $HEADER = $self->{HEADER}."\n"; } sub setInputRequest { my $self = shift; if(@_) { $self->{INPUT_REQUEST} = shift } $INPUT_REQUEST = $self->{INPUT_REQUEST}." "; } sub addItem { my $self = shift; if(@_) { $self->{ITEM} = shift } push(@MENU_ITEMS, $self->{ITEM}); } sub getMenu { my $formatted_menu .= $HEADER; my $it=1; foreach(@MENU_ITEMS) { $formatted_menu.=$it.". ".$_."\n"; $it++ } $formatted_menu.=$INPUT_REQUEST; return $formatted_menu; } 1; ``` If I call the following perl script: ``` #!/usr/bin/perl use strict; use Menu; my $menu = Menu->new(); $menu->addItem("First Option"); $menu->addItem("Second Option"); print $menu->getMenu; ``` I'll get the following output: ``` Pick one of the options below 1. First Option 2. Second Option Type your selection: ``` I'd like to modify given class in a way that I can pass a second argument to the method `addItem()` something like: `$menu->addItem("First Option", &firstOptionFunction());` and if and only if `First Option` is selected, then `$firstOptionFunction` is executed. Is there any way to achieve such behavior in Perl? Thanks!

Original source