http://www.perlmonks.org?node_id=1030627


in reply to Perl 5.17 change to use re 'eval' breaks Acme::EyeDrops

Shorn of its obfuscation, that code is equivalent to
'' =~ '(?{eval"print\"hello world\\n\""})';
Note that the pattern is within a string literal ('') rather than a pattern literal (//). The 5.17.x changes make it so that code blocks which don't need a 'use re eval' can appear only within pattern literals.

Dave.