Types, bindings, and null safety

The idea

Dart variables have types even when var lets the compiler infer them. final permits a binding to be assigned once, while const creates a compile-time constant value where a constant expression is available. Neither keyword is a substitute for understanding the object being referenced: a final list can still be mutable. Nonnullable types exclude null unless a question mark marks the type as nullable.

The operator ?? supplies a fallback only for null, not for zero or an empty string. Use ?. when accessing a member through a possibly absent receiver. For arithmetic, / produces division with a fractional result, while ~/ truncates the quotient toward zero. Select the operation from the requirement instead of relying on the destination variable to fix it.

void main() {
  int? stored;
  final count = stored ?? 7;
  print(count ~/ 2);
  print(count / 2);
}

3
3.5

The uninitialized nullable local starts as null, so count becomes seven. The two division operators deliberately request different results.