Hack #57. Name Your Anonymous Subroutines
Trade a little anonymity for expressivity.
Despite the apparently oxymoronic name, "named anonymous subroutines" are an undocumented feature of Perl. Originally described by "ysth" on Perl Monks, these are a wonderful feature.
Suppose your program merrily runs along with a carefree attitudeâbut then dies an ugly death:
Denominator must not be zero! at anon_subs.pl line 11 main::__ANON__(0) called at anon_subs.pl line 17
What the heck is main::__ANON__(0)
? The answer may be somewhere in code such as:
use Carp; sub divide_by { my $numerator = shift; return sub { my $denominator = shift; croak "Denominator must not be zero!" unless $denominator; return $numerator / $denominator; }; } my $seven_divided_by = divide_by(7); my $answer = $seven_divided_by->(0);
In this toy example, it's easy to see the problem. However, what if you're generating a ton of those divide_by
subroutines and sending them all throughout your code? What if you have a bunch of subroutines all generating subroutines (for example, if you've breathed too deeply the heady fumes of Mark Jason Dominus' Higher Order Perl book)? Having a bunch of subroutines named __ANON__
is very difficult to debug.
Tip
$seven_divided_by
is effectively a curried version of divide_by(â)
. That is, it's a function that already has one of multiple arguments bound to it. There's a piece of random functional programming jargon to use to impress people.
The Hack
Creating an anonymous subroutine creates ...
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