sort can take a subroutine name as its first argument. The subroutine performs the comparison and returns the negative, positive or zero result. The delta you've linked to says that as of 5.10.0 such subroutines may now be recursive.

I've investigated the deltas because of Syntax::Construct and it seemed it had been possible to use recursive subroutines in older Perls, too. 5.10 was just the version that documented the fact.
map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

Hah. I didn't know that. I have exclusively used the BLOCK form to this date. It's nice being able to refer to a sub by name, but when is it useful that sub being able to recurse?


holli

You can lead your users to water, but alas, you cannot drown them.

> but when is it useful that sub being able to recurse?

what comes to mind are chained comparisons in sort °

 
sort { 
        $a->[0] cmp $b->[0]  
     or $a->[1] cmp $b->[1]       # *
     or $a->[2] cmp $b->[2]       # *
     or ...                       # *
    } @AoA

# *) only check if former was equal == 0 == false
[download]

if you don't know the number of fields, recursive comparisons come in handy.

I'm bu-la-zy, so constructing the recursion is left as exercise. ;-)

HTH!

update

In hindsight ... this particular case could also be solved in a loop.

So think about a more complicated data structures like trees to be sorted.

In the end it's about convenience ... every loop can be expressed as recursion and vice versa.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

°) see examples in code from line 39 onwards

Just a guess ... This might be related to the "newish" feature of having a special variable holding the reference of the current sub to facilitate recursions.

Unfortunately I wasn't able to find it again in order to test if it has issues with older sort implementations.

update

__SUB__ it was.

not a variable though ...

IIRC, __SUB__ was introduced in 5.12 5.16, so it's not likely relevant.

Perl 5.16

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}