#!/bin/perl -p
BEGIN { $FIELD="field1|field2|field3"; }
s/(\$\w+(?:\[\d\])?)->($FIELD)\b(?!\()/$1\->\{$2\}/g;
s/(\$\w+(?:\[\d\])?)->set_($FIELD)\(([^)]*)\)/$1\->\{$2\}= $3/g;