use v5.12;
use warnings;


say "-"x10, ' ?';
for my $i (1..3) {
  say "Match $i" if
    '2' =~ m/(?{say "in $i"})$i/;
}


say "-"x10, ' ??';
for my $i (1..3) {
  say "Match $i" if
    '2' =~ m/(??{say "in $i";$i})/;
}


##</code><code>##

# This is perl 5, version 40, subversion 3 (v5.40.3) built for aarch64-android

Compilation started at Sat Apr 18 20:38:08

perl tst_re.pl 
---------- ?
in 2
Match 2
---------- ??
in 1
in 1
in 2
Match 2
in 3
in 3

Compilation finished at Sat Apr 18 20:38:08, duration 0.03 s