I think the for someone who is not very familiar with map, the Schwartzian Transform is a complete mystery. It took me seeing map in action to appreciate its usefulness. So, in the interest of opening a novice's eyes...
The map function is one of Perl's more wonderous keywords. It's in my list of Perl Milestones of Enlightenment - mysterious at first, powerful yet simple in its action.
map takes two arguments: an operation of some sort (no pun intended) like a single keyword or a code block (as is used in this case). And a list to operate on. The example given in the pod offers:@chars = map(chr, @nums);. Which takes the list of @nums and performs the chr function on them and assigns the new array to @chars. Or, rewritten with a code block: @chars = map {chr}, @nums; Look right to left, bottom to top, to see the progression. On to the routine...
So what happens in Hofmator's implementation is every element in the list @unsorted goes through the code block of:
/^([+-])(\d+)h(\d+)m$/; [$_, sprintf("%s%d",$1,$2*60+$3)]
The regex splits up the string into +-, hours, and minutes, and the second half creates an anonymous array out of it: first element being the original string, $_, the second being the total minutes of the string.
Sort does its magic, sorting on the second element (that's 1). No calculation of minutes needed - already done by the map.
Then the map closest to the @sorted assignment takes the annonymous array, taking just the first element (the original string).
There's your sorted list of time strings with the minute calculation performed only once per array element.
HTH
-Ducky | 