how could "modifying the input list" have any side-effects here?

You'd be surprised in some instances. 

$ perl -le'
   for (1..2) {
      print map { my $x=$_; $_="!"; $x } 1..5
   }
'
12345
!!!!!

[download]

But that's not the case here.

I can see no bad practice in rewriting a hash and a sorted list of its keys in one pass: 

%hash = map { my $v = $hash{$_}; s/ /_/g; $_, $v } @sorted;

[download]

That was actually hard to understand, but I suppose a comment would solve that.

Keep in mind that perlcritic will err on the side of false positive over false negative. Otherwise, it would be redundant with -w. Even if the rule is sound doesn't mean there aren't exceptions.

In reply to Re^2: PerlCritic, $_ and map by ikegami
in thread PerlCritic, $_ and map by chexmix

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