visitChildren method Null safety
Implementation
void visitChildren(void Function(int, ArgDone) f, [int offset = 0]) {
int n = 0;
for (final c in _next) {
f(offset + n++, c);
}
final nd = _nextOnDot;
if (nd != null) {
final da = nd.child as DigitArg;
da.visitChildren(f, n);
}
}