Think Globally, Play With Hashes Locally

Reading a bit from Effective Perl Programming, I found out that Perl 5.12 supports deleting an element in a hash in a local scope. I was looking up from Higher Order Perl for a moment, so you might guess that my thoughts went to manipulating dispatch tables.

my %subs = ( do  => sub { return 'c' },
             rey => sub { return 'd' },
             mi  => sub { return 'e' },
             fa  => sub { return 'f' },
             so  => sub { return 'g' },
             la  => sub { return 'a' },
             ti  => sub { return 'b' }, ) ;

my @notes = qw( do rey mi fa so la ti do rum fmep agog ) ;

{
    delete local $subs{ ti } ;
    say '=' x 20 ;
    for my $note ( @notes ) {
        if ( $subs{ $note } ) {
            my $sub = $subs{ $note } ;
            say join "\t", '', $note, &$sub ;
            }
        }
    }

say '-' x 20 ;
for my $note ( @notes ) {
    if ( $subs{ $note } ) {
        my $sub = $subs{ $note } ;
        say join "\t", '', $note, &$sub ;
        }
    }

====================
 do c
 rey d
 mi e
 fa f
 so g
 la a
 do c
--------------------
 do c
 rey d
 mi e
 fa f
 so g
 la a
 do c

Yeah, I'm still on 5.10. But that made me think.
Can you add to a hash only in the local scope?

my %subs = ( do  => sub { return 'c' },
             rey => sub { return 'd' },
             mi  => sub { return 'e' },
             fa  => sub { return 'f' },
             so  => sub { return 'g' },
             la  => sub { return 'a' },
             ti  => sub { return 'b' }, ) ;

my @notes = qw( do rey mi fa so la ti do rum fmep agog ) ;

{
    local $subs{ rum } = sub { return 'one' }  ;
    say '=' x 20 ;
    for my $note ( @notes ) {
        if ( $subs{ $note } ) {
            my $sub = $subs{ $note } ;
            say join "\t", '', $note, &$sub ;
            }
        }
    }

say '-' x 20 ;
for my $note ( @notes ) {
    if ( $subs{ $note } ) {
        my $sub = $subs{ $note } ;
        say join "\t", '', $note, &$sub ;
        }
    }

====================
 do c
 rey d
 mi e
 fa f
 so g
 la a
 ti b
 do c
 rum one
--------------------
 do c
 rey d
 mi e
 fa f
 so g
 la a
 ti b
 do c

Yeah, I'm still on 5.10. But that made me think.
And you might guess that it's a foregone conclusion that you can modify a hash element locally.

my %subs = ( do  => sub { return 'c' },
             rey => sub { return 'd' },
             mi  => sub { return 'e' },
             fa  => sub { return 'f' },
             so  => sub { return 'g' },
             la  => sub { return 'a' },
             ti  => sub { return 'b' }, ) ;

my @notes = qw( do rey mi fa so la ti do rum fmep agog ) ;

{
    #delete local $subs{ ti } ;
    #local $subs{ rum } = sub { return 'one' }  ;
    local $subs{ ti } = sub { return 'FMEP' }  ;
    say '=' x 20 ;
    for my $note ( @notes ) {
        if ( $subs{ $note } ) {
            my $sub = $subs{ $note } ;
            say join "\t", '', $note, &$sub ;
            }
        }
    }

say '-' x 20 ;
for my $note ( @notes ) {
    if ( $subs{ $note } ) {
        my $sub = $subs{ $note } ;
        say join "\t", '', $note, &$sub ;
        }
    }

====================
 do c
 rey d
 mi e
 fa f
 so g
 la a
 ti FMEP
 do c
--------------------
 do c
 rey d
 mi e
 fa f
 so g
 la a
 ti b
 do c

The more I play with dispatch tables, the more I imagine practical uses of this. I love cool stuff!