Question

Is it possible to define anonymous subroutines in a hash constructor in Perl?

I’m trying to do something like this:

my %array = { one   => sub { print 'first $_[0]' },               two   => sub { print 'next  $_[0]' },               three => sub { print 'last  $_[0]' }};  $array{$foo}->('thing'); 

But it isn’t working. The code seems to run and compile, but the values in the array are blank. If I do this:

my %array;  $array{'one'}   = sub { print 'first $_[0]' }; $array{'two'}   = sub { print 'next  $_[0]' }; $array{'three'} = sub { print 'last  $_[0]' };  $array{$foo}->('thing'); 

Then it seems to work fine. So I have a workaround, but it’s just bugging me and I wondered if anyone knows whether it’s possible and, if so, what the syntax is.

Answer 1

It looks like you’re assigning into the hash incorrectly. Using {} constructs an anonymous hash reference, which you assign to a scalar. But you’re assigning to a named hash (%array).

You need to assign into a scalar:

my $array = { one   => sub { print 'first $_[0]' },               two   => sub { print 'next  $_[0]' },               three => sub { print 'last  $_[0]' }};  $array->{$foo}->('thing'); 

Or to not use the anon constructor syntax:

my %array = ( one   => sub { print 'first $_[0]' },               two   => sub { print 'next  $_[0]' },               three => sub { print 'last  $_[0]' });  $array{$foo}->('thing');