!7

!include once #1019844 // BetterStringBuffer

p-exp {
  new BetterStringBuffer buf;
  final Var<Int> count = new(0);
  buf.onChange = ll(r { incIntVar(count) });
  
  assertEquals(0L, buf.changes);
  buf.append("yo");
  assertEquals(1L, buf.changes);
  buf.append(' ');
  buf.append("what");
  assertEquals(3L, buf.changes);
  assertEquals(3, count!);
  assertEqualsVerbose("yo what", str(buf));
}