Abstraction and Subroutines

For me, the subroutine is the unit of abstraction. Give me subroutines (or methods or functions) and I can change the world.

Fixing Hashes

If you try and retrieve a non-existent key from a perl hash, it returns an undefined value. Often, that isn’t what I want.

No worries. With a simple subroutine, I can fix it.

sub get_hash_value (\%$)
{
    my ($hash_ref, $key) = @_;
    if (! exists $hash_ref->{$key}) {
        die "KeyNotExists: $key\n";
    }
    return $hash_ref->{$key};
}

my %hash;
print $hash{'hardtospellkey'};
print get_hash_value(%hash, 'hardtospeelkey');

With warnings turned on, this is easily caught. Plus with emacs dabbrev, it is never a problem for me anyway – my mispellings are consistent.

But with a less enlightened language than perl, if you have this problem then as long as you also have subroutines, you can fix it.

Use of uninitialized value $hash{"hardtospellkey"} in print at t.pl line 14.
KeyNotExists: hardtospeelkey

Fixing Weakly Typed Numbers

use Scalar::Util 'looks_like_number';

sub ensure_number
{
    my $val = shift;
    if (! looks_like_number($val)) {
        die "NotNumber: $val\n";
    }
    return $val;
}

my $x = '1';
my $y = 'rhubarb';

print ensure_number($x) + ensure_number(2), "\n";
print ensure_number($x) + ensure_number($y), "\n";

In production code I’m likely to call that subroutine something more like _n.

3
NotNumber: rhubarb

Subroutine Call Speed

This is why I care about perl subroutine call speed – I have so many little routines stating exactly what I expect from my code. And it seems like it is quick enough.

It would be nice though to have something like emacs’ defsubst. Say a new keyword like inline_sub { ... }. So I can invent the syntax I want, secure in the knowledge that, code bloating aside, I’m not paying for it.

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