svoid tok_swappableFunctions(LS tok) {
  int i;
  while ((i = jfind(tok, "swappable <id> <id>() {")) >= 0) {
    S returnType = tok.get(i+2), name = tok.get(i+4);
    S base = name + "_base";
    int iCurly = indexOf(tok, i, "{");
    replaceTokens_reTok(tok, i, iCurly+1, "transient IF0<\*returnType*/> \*name*/;\n" + 
      "\*returnType*/ \*name*/() { ret \*name*/ != null ? \*name*/! : \*base*/(); }\n" +
      "\*returnType*/ \*base*/() {");
  }
}

Began life as a copy of #1026384