package TieTest;

sub TIESCALAR {
    my $class = shift @_;
    die "Incorrect # of arguments" if @_ % 2;
    my $self = bless {}, $class;
    $self->_init(@_);
    return $self;
}

sub FETCH {
    my $self = shift @_;
    my $work_around = sub {
        my $tgt = shift @_;
        if (exists $self->{$tgt}) {
            print "Fetching value from cache\n";
            return $self->{$tgt};
        }
        print "Calculating and caching value for $tgt\n";
        return $self->{$tgt} = $self->{subref}->($tgt);
    };
    return $work_around;
}

sub _init {
    my $self = shift @_;
    my %arg = @_;
    for (qw/subref/) { # All valid args
        $self->{$_} = delete $arg{$_};
    }
    if (keys %arg) {
        my $bad = join ' ', keys %arg;
        die "The following args are invalid: $bad";
    }
    return;
}


package main;
tie my $tied_func, 'TieTest', subref => sub {$_[0] * 2}; 

# Calculate the function values for 1 .. 100
print $tied_func->($_), "\n" for 1 .. 10;

# Retrieve cached values
print $tied_func->($_), "\n" for 1 .. 10;
[download]