hash = (
        b => ($b =~ /\d/    ? 1  : 0),
        a => ($b =~ /(\d+)/ ? $1 : 0),
);

##</code><code>##

hash = (
        a => ($b =~ /(\d+)/)[0] || 0,
        b => ($b =~ /\d/    ? 1  : 0)
);

##</code><code>##

$ perl -wE 'sub f {say @_} 3 =~ /(\d)/; f $1'
3
$ perl -wE 'sub f {"1" =~ "1"; say @_} 3 =~ /(\d)/; f $1'
Use of uninitialized value $_[0] in say at -e line 1.
$ perl -wE 'sub f {"1" =~ "1"; say @_} 3 =~ /(\d)/; f "$1"'
3
$