var, final and const in Dart

Three ways to bind: mutable, once at run time, fixed at compile time.

void main() {
  // var infers and stays mutable; final binds once at run time;
  // const is fixed at compile time.
  var sightings = 12;
  sightings += 1;
  final opened = DateTime.now();
  const perch = 'north fence';

  // A type annotation replaces var when inference needs steering.
  double meanPerHour = sightings / 4;
  print('$sightings from the $perch since $opened');
  print('Rate: ${meanPerHour.toStringAsFixed(1)} per hour');
}

How it works

1. var infers and stays assignable; += updates it.
2. final binds once when the line runs — DateTime.now() is fine.
3. const must be known at compile time; annotations replace var when needed.

Keywords and builtins used here

• const
• double
• final
• var
• void

The run, in numbers

Lines

13

Characters to type

421

Tokens

72

Three-star pace

70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 62 seconds.

Type this snippet

Step 2 of 3 in Values, step 2 of 27 in Language basics.

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