Or get slower lexical variables for $a and $b by providing a prototyping your comparison function and creating my variables to store them in.

From perlfunc(1):

sort SUBNAME LIST
sort BLOCK LIST
sort LIST

  Sorts the LIST and returns the sorted list value.
  ...
  If the subroutine's prototype is "($$)", the ele­
  ments to be compared are passed by reference in
  "@_", as for a normal subroutine.  This is slower
  than unprototyped subroutines, where the elements
  to be compared are passed into the subroutine as
  the package global variables $a and $b (see exam­
  ple below).

But that will make the code non-portable. I believe that feature was introduced as recently as 5.6, but I could be mistaken. I know it wasn't in 5.4.

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

See the output of the following two one-liners:

perl -MO=Xref -e "my @array = sort { $a <=> $b } ( 2, 8, 3 );"
[download]

perl -MO=Xref = "local ( $a, $b ); my @array = sort { $a <=> $b } ( 2,
+ 8, 3 );"
[download]

The first example results in crossreference output that essentially makes no mention of $a and $b.

The second example results in crossreference output that includes $a and $b under the package main namespace.




Dave

If you're confused about variables and packages, it sounds like you need to read Coping with Scoping.

Since sort was there in Perl 4, the mechanism that it uses by default ($a, $b) accesses the package variable of that name in the current package.