> If I use map, it is understood that there are to be no modifications to the original data set

I was meditating if map should be changed in this respect.

Questions:

• are there use cases where a new list is returned and the old list needs to be altered by alias?
• if yes, should we introduce a non aliasing default var to avoid this trap? something like $__ or so?

The usual workaround is to copy $_, like in

   DB<111> @b = map {my $x=$_; ++$x} @a
 => (2 .. 11)

 DB<112> @a
 => (1 .. 10)
[download]

Then again its pretty easy to replace ++$_ with $_+1 and s/x/y/ with s/x/y/r in current Perl versions.

Not sure if there are any modifying operators left without a non-modifying counterpart.