in reply to Re^3: is perl's regular expression engine reentrant ? (works)
in thread is perl's regular expression engine reentrant ?

With the extensive rewrite of the regular expression engine, by dave_the_m and demerphq, that particular expression works just fine in the development version (what will become 5.10).

% perl5.9.5 -wle  'print +("_" =~ m{(??{"_" =~ /./})}) ? 1 : 0'
0

% perl5.9.5 -wle 'print +("_" =~ m{(??{"_" !~ /./})}) ? 1 : 0'
1

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There exist, however, more exotic code constructs that will trip up reentrancy bugs.

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