---> Pass constant assignment by reference:
string(10) "a.original"
string(10) "a.original"


---> Pass variable assignment by reference:
string(10) "a.original"
string(10) "a.original"


---> Pass reference assignment by reference:
string(10) "a.original"
string(9) "a.changed"


---> Pass concat assignment by reference:
string(20) "b.originala.original"
string(10) "a.original"